Troubleshooting Amazon Lex bots that misunderstand callers in Amazon Connect

See also

Sources

1. 1
   When a Lex V2 alias is repointed to a new version, in-progress sessions continue on the current version and only new sessions use the new version.

   Versioning and aliases with your Lex V2 bot · Aliases for your Lex V2 bot, closing Note · Checked 2026-10-02
2. 2
   When bot intents do not appear in the flow designer, AWS directs administrators to verify that Use in flow and flow modules is enabled on the bot alias in the Connect admin website.

   Flow block in Connect Customer: Get customer input · Configure for Amazon Lex input, Intents, Check if the version is associated with the alias (steps 1-2) · Checked 2026-10-02
3. 3
   The Lex V2 session attribute x-amz-lex:allow-dtmf-input defaults to true; if set to false the bot does not accept DTMF input for the scoped intent and slot.

   Configuring timeouts for capturing user input with a Lex V2 bot · Set configuration for DTMF input, Allow DTMF input · Checked 2026-10-02
4. 4
   When a Check contact attributes block branches on a Lex V2 alternative intent, the intent name is case sensitive and must exactly match the name in Lex.

   Flow block in Connect Customer: Check contact attributes · Amazon Lex V2 attributes, Alternative Intents, item 1 · Checked 2026-10-02
5. 5
   Amazon Lex V2 returns the most likely intent plus up to 4 alternative intents with confidence scores in each response's interpretations.

   Using intent confidence scores to improve intent selection with Lex V2 · Paragraph before the interpretations JSON example · Checked 2026-10-02
6. 6
   When bot intents do not appear in the flow designer, AWS directs administrators to add the tag AmazonConnectEnabled = True on the bot in the Amazon Lex console and then refresh the flow designer.

   Flow block in Connect Customer: Get customer input · Configure for Amazon Lex input, Intents, Check whether the AmazonConnectEnabled tag is set to True (steps 1-3) · Checked 2026-10-02
7. 7
   Lex V2 input session attribute keys follow x-amz-lex:<InputType>:<BehaviorName>:<IntentName>:<SlotName>, where * applies a default to all intents or slots and intent- or slot-specific settings take precedence over the default.

   Configuring timeouts for capturing user input with a Lex V2 bot · Introductory section, configuration key syntax · Checked 2026-10-02
8. 8
   Only one set of Lex session attributes applies per conversation, and precedence is Lambda-provided attributes, then attributes set in the Get customer input block, then service defaults.

   Flow block in Connect Customer: Get customer input · Additional configuration tips, order of precedence list · Checked 2026-10-02
9. 9
   For Amazon Lex Classic bots in Connect, barge-in was disabled by default and had to be enabled with x-amz-lex:barge-in-enabled; that attribute does not control DTMF barge-in.

   Flow block in Connect Customer: Get customer input · Barge-in configuration and usage for Amazon Lex, Amazon Lex (Classic) tab · Checked 2026-10-02
10. 10
    For Amazon Lex V2 bots, barge-in is enabled by default and can be changed per intent and slot with the x-amz-lex:allow-interrupt session attribute.

    Configuring timeouts for capturing user input with a Lex V2 bot · How interrupt behavior works in a Lex V2 bot · Checked 2026-10-02
11. 11
    Amazon Lex Classic bots used different timeout attribute names in Connect: x-amz-lex:max-speech-duration-ms, x-amz-lex:start-silence-threshold-ms and x-amz-lex:end-silence-threshold-ms.

    Flow block in Connect Customer: Get customer input · Configurable time-outs for voice input, Amazon Lex (Classic) tab · Checked 2026-10-02
12. 12
    AWS describes Lex V2 intent confidence scores as comparative values that should not be relied on as absolute scores and that may change as Lex V2 improves.

    Using intent confidence scores to improve intent selection with Lex V2 · Introductory section, paragraph beginning The confidence scores that Amazon Lex V2 returns · Checked 2026-10-02
13. 13
    For Lex bots used from Connect, the DTMF end character defaults to # and the DTMF deletion character, which clears accumulated digits and ends the utterance, defaults to *.

    Configuring timeouts for capturing user input with a Lex V2 bot · Set configuration for DTMF input, Deletion character and End character · Checked 2026-10-02
14. 14
    The Lex DTMF end timeout x-amz-lex:dtmf:end-timeout-ms defaults to 5000 milliseconds, so callers who are not told to finish with # wait about five seconds before Lex stops collecting key presses.

    Flow block in Connect Customer: Get customer input · Configurable fields for DTMF input, End timeout; Additional configuration tips, bullet on pound key · Checked 2026-10-02
15. 15
    The maximum number of DTMF digits per Lex utterance, x-amz-lex:dtmf:max-length, defaults to 1024 and cannot be increased, though it can be set lower.

    Configuring timeouts for capturing user input with a Lex V2 bot · Set configuration for DTMF input, Maximum number of DTMF digits per utterance · Checked 2026-10-02
16. 16
    DTMF input that Connect passes to a Lex bot is exposed as the request attribute x-amz-lex:dtmf-transcript (up to 1024 characters); input ending with the deletion character yields [DEL] rather than the digits.

    Flow block in Connect Customer: Get customer input · Additional configuration tips, DTMF input scenarios table · Checked 2026-10-02
17. 17
    The Lex V2 end silence timeout x-amz-lex:audio:end-timeout-ms, which controls how long the bot waits after the caller stops speaking before treating the utterance as finished, defaults to 600 milliseconds.

    Configuring timeouts for capturing user input with a Lex V2 bot · Set the timeouts for voice input, Silence timeout · Checked 2026-10-02
18. 18
    Amazon Lex V2 returns AMAZON.FallbackIntent as the top intent when every intent's confidence is below the confidence threshold, or when FallbackIntent's interpretation confidence is higher than all other intents.

    Using intent confidence scores to improve intent selection with Lex V2 · AMAZON.FallbackIntent section · Checked 2026-10-02
19. 19
    For the chat channel, the Get customer input block is supported only when Amazon Lex is used; otherwise the contact takes the Error branch.

    Flow block in Connect Customer: Get customer input · Contact types table, Chat row · Checked 2026-10-02
20. 20
    The Get customer input block routes a contact down the Default branch when the input does not match any configured DTMF condition or any intent configured on the block for the Lex bot.

    Flow block in Connect Customer: Get customer input · Flow block branches, item 2 (Default) · Checked 2026-10-02
21. 21
    The Get customer input block takes the Error branch when the block runs but errors for DTMF, or when an intent is not fulfilled in the Amazon Lex V2 bot.

    Flow block in Connect Customer: Get customer input · Flow block branches, item 3 (Error) · Checked 2026-10-02
22. 22
    The Get customer input Timeout branch is taken when no input arrives within the Lex V2 chat timeout or within the Set timeout value configured for DTMF.

    Flow block in Connect Customer: Get customer input · Flow block branches, item 1 (Timeout) · Checked 2026-10-02
23. 23
    A Lex V2 bot that recognizes callers well in the console test window can still behave differently on Connect calls, because the test window uses 16 kHz audio while contact-center audio is 8 kHz and some recognition features apply only at 8 kHz.inferred

    Improving recognition of slot values with runtime hints in the conversation · Runtime hints basics, last bullet (16 kHz test window vs 8 kHz contact center) · Checked 2026-10-02
24. 24
    A timeout or barge-in value set in the Get customer input block can appear to be ignored if the bot's Lambda code hook returns the same session attribute, because Lambda-provided attributes take precedence.inferred

    How flow blocks use Amazon Lex session attributes · Life cycle of session attributes · Checked 2026-10-02
25. 25
    Connect flows can branch on the Lex V2 Intent Confidence Score, which is expressed on a scale from 0 (not at all confident) to 1 (100 percent confident).

    Flow block in Connect Customer: Check contact attributes · Amazon Lex V2 attributes, Intent Confidence Score · Checked 2026-10-02
26. 26
    The Get customer input Intents dropdown does not list intents for Amazon Lex V1 bots, cross-region bots, or bots whose ARN is set dynamically.

    Flow block in Connect Customer: Get customer input · Configure for Amazon Lex input, Intents, paragraph beginning The Intents dropdown box does not list · Checked 2026-10-02
27. 27
    For intents to be listed in the Get customer input Intents dropdown, the Lex bot must have a Connect tag and the bot alias must have a version associated with it.

    Flow block in Connect Customer: Get customer input · Configure for Amazon Lex input, Intents, Add intent · Checked 2026-10-02
28. 28
    If Lex timeout attributes are set only in the Lex Lambda function rather than in the Get customer input block, default values apply until the Lex bot is invoked.

    Flow block in Connect Customer: Get customer input · Additional configuration tips, bullet beginning To control time-out functionality · Checked 2026-10-02
29. 29
    AWS discontinued support for Amazon Lex V1 on September 15, 2025, after which the Lex V1 console and V1 resources are no longer accessible.

    Add an Amazon Lex bot to Connect Customer · Important: End of support notice, top of page · Checked 2026-10-02
30. 30
    With an Amazon Lex V2 bot, the Connect contact's language attribute must match the language model used to build the bot, set with a Set voice block or a Set contact attributes block; Lex Classic did not have this requirement.

    Add an Amazon Lex bot to Connect Customer · Create a flow and add your Amazon Lex bot, Important note · Checked 2026-10-02
31. 31
    Each Lex V2 log entry's bot object records the alias id and name, locale id and bot version that handled the utterance.

    Viewing text logs in Amazon CloudWatch Logs from Lex V2 · JSON schema, bot object (aliasId, aliasName, localeId, version) · Checked 2026-10-02
32. 32
    Lex V2 log entries include a responseReason field whose value StartTimeout marks a server-generated response when the user did not provide input, and a bargeIn field indicating whether the input interrupted the previous bot response.

    Viewing text logs in Amazon CloudWatch Logs from Lex V2 · Field list, bargeIn and responseReason · Checked 2026-10-02
33. 33
    Lex V2 text log entries include inputTranscript (the text Lex derived from speech, or the key pressed for DTMF), inputMode (DTMF, Speech or Text), and a transcriptions list of candidate transcriptions.

    Viewing text logs in Amazon CloudWatch Logs from Lex V2 · Field list, inputTranscript, transcriptions and inputMode · Checked 2026-10-02
34. 34
    Lex V2 conversation logs cannot be used with a bot that is subject to COPPA.

    Logging conversations with conversation logs in Lex V2 · Overview, Note · Checked 2026-10-02
35. 35
    Lex V2 conversation logs are configured per bot alias: text logs (including transcripts of audio input and metadata) go to CloudWatch Logs and audio logs go to Amazon S3.

    Logging conversations with conversation logs in Lex V2 · Overview, paragraph beginning Conversation logs are configured for an alias · Checked 2026-10-02
36. 36
    The Amazon Connect Get customer input documentation states that the Lex V2 max speech duration attribute x-amz-lex:audio:max-length-ms defaults to 12000 milliseconds.disputed

    Flow block in Connect Customer: Get customer input · Configurable time-outs for voice input, Amazon Lex tab, Max Speech Duration · Checked 2026-10-02
37. 37
    The Amazon Lex V2 developer guide states that x-amz-lex:audio:max-length-ms defaults to 55,000 milliseconds, which is also its maximum.disputed

    Configuring timeouts for capturing user input with a Lex V2 bot · Set the timeouts for voice input, Maximum utterance length · Checked 2026-10-02
38. 38
    The Amazon Connect documentation states that setting Max Speech Duration above 55000 milliseconds routes the contact down the Error branch of Get customer input.disputed

    Flow block in Connect Customer: Get customer input · Configurable time-outs for voice input, Max Speech Duration, Important note · Checked 2026-10-02
39. 39
    The Amazon Lex V2 developer guide states that a max-length-ms value above 55,000 milliseconds is reset to 55,000 milliseconds.disputed

    Configuring timeouts for capturing user input with a Lex V2 bot · Set the timeouts for voice input, Maximum utterance length, final sentence · Checked 2026-10-02
40. 40
    Each Lex V2 text conversation log entry carries a missedUtterance flag, and when it is true the intent, slots and slotToElicit fields are omitted from the entry.

    Viewing text logs in Amazon CloudWatch Logs from Lex V2 · Field list, missedUtterance; notes after the JSON schema, first bullet · Checked 2026-10-02
41. 41
    Lex V2 runtime hints are supported only for 8 kHz audio such as contact center integrations, and are not applied in the Lex console test window, which uses 16 kHz audio.

    Improving recognition of slot values with runtime hints in the conversation · Runtime hints basics, last bullet · Checked 2026-10-02
42. 42
    Lex V2 runtime hints are available only in English (US) and English (UK), only for slot elicitation, and only for custom slot types and the AMAZON.City, Country, FirstName, LastName, State and StreetName types.

    Improving recognition of slot values with runtime hints in the conversation · Introductory section and Runtime hints basics · Checked 2026-10-02
43. 43
    The Lex V2 sentiment score used by Get customer input sentiment override is based on the caller's last utterance, not the whole conversation, and a negative threshold is evaluated before a positive one.

    Flow block in Connect Customer: Get customer input · Configure for Amazon Lex input, Use sentiment override · Checked 2026-10-02
44. 44
    If a flow uses a non en-US voice with an Amazon Lex V2 bot and Set language attribute is not selected in the Set voice block, the Get customer input block results in an error.

    Flow block in Connect Customer: Set voice · Use an Amazon Lex V2 bot with Connect Customer, second bullet · Checked 2026-10-02
45. 45
    The Set voice block does not validate the language code: an invalid code does not take the Set voice Error branch but can cause erroneous behaviour with Lex V2 bots.

    Flow block in Connect Customer: Set voice · Properties, Tip; Configuration Examples table, ar-AE with Ruth row · Checked 2026-10-02
46. 46
    In Lex V2, input that mixes single letters and phonetic words (for example x as in x-ray i u) requires the spell-by-word style; spell-by-letter will not recognize it.

    Capturing slot values with spelling styles during the conversation · Paragraph after Default style description · Checked 2026-10-02
47. 47
    Lex V2 spell-by-letter and spell-by-word slot elicitation styles cannot be enabled in the console; they are set at runtime through slotElicitationStyle in an ElicitSlot dialogAction, via the runtime APIs or a Lambda function.

    Capturing slot values with spelling styles during the conversation · Enabling spelling, including Note · Checked 2026-10-02
48. 48
    The Amazon Connect documentation states that the Lex V2 start silence threshold x-amz-lex:audio:start-timeout-ms defaults to 3000 milliseconds.disputed

    Flow block in Connect Customer: Get customer input · Configurable time-outs for voice input, Amazon Lex tab, Start Silence Threshold · Checked 2026-10-02
49. 49
    The Amazon Lex V2 developer guide states that the voice timeout x-amz-lex:audio:start-timeout-ms defaults to 4,000 milliseconds.disputed

    Configuring timeouts for capturing user input with a Lex V2 bot · Set the timeouts for voice input, Voice timeout · Checked 2026-10-02
50. 50
    Amazon Lex V2 allows at most 2 concurrent voice-mode StartConversation conversations on TestBotAlias (not adjustable), against a default of 400 for other aliases (adjustable).

    Quotas (Amazon Lex V2 Developer Guide) · Runtime quotas table, rows for concurrent voice-mode conversations for StartConversation · Checked 2026-10-02
51. 51
    The Lex V2 TestBotAlias is always associated with the Draft version of the bot and is intended only for manual testing.

    Versioning and aliases with your Lex V2 bot · The Draft version of your Lex V2 bot; Aliases for your Lex V2 bot · Checked 2026-10-02
52. 52
    AWS instructs that production Connect flows use a Lex alias other than TestBotAlias, because TestBotAlias supports only a limited number of concurrent calls.

    Add an Amazon Lex bot to Connect Customer · Create an alias for the bot, Amazon Lex tab, Important note · Checked 2026-10-02
53. 53
    The Lex V2 confidence threshold is a value from 0.00 to 1.00 set per bot language (locale), in the console Language details or through nluIntentConfidenceThreshold on CreateBotLocale or UpdateBotLocale.

    Using intent confidence scores to improve intent selection with Lex V2 · Setting and changing the confidence threshold · Checked 2026-10-02
54. 54
    When touchtone buffering is enabled, a Get customer input block in Amazon Lex mode clears the buffer before the bot interaction, so digits the caller pressed ahead are not used.

    Flow block in Connect Customer: Get customer input · Touchtone buffering, second bullet · Checked 2026-10-02
55. 55
    Lex V2 audio transcription confidence scores, with up to three candidate transcriptions sent to the Lambda code hook, are available only for en-GB and en-US and only for 8 kHz audio.

    Using voice transcription confidence scores to improve conversations with your Lex V2 bot · Paragraph beginning Audio transcription confidence scores are available only; JSON structure introduction · Checked 2026-10-02
56. 56
    Amazon Lex V2 voice timeout session attributes use the x-amz-lex:audio namespace: max-length-ms, start-timeout-ms and end-timeout-ms.

    Configuring timeouts for capturing user input with a Lex V2 bot · Set the timeouts for voice input · Checked 2026-10-02
57. 57
    A Lex V2 bot locale has a speechDetectionSensitivity setting for voice activity detection with values Default, HighNoiseTolerance and MaximumNoiseTolerance, intended to tune how the bot responds to background noise.

    CreateBotLocale - Amazon Lex V2 API Reference · Request Body, speechDetectionSensitivity · Checked 2026-10-02
58. 58
    A Lex V2 bot version that is not used for six months is marked inactive, runtime operations fail against it, and it is reactivated by rebuilding all of its languages.

    Versioning and aliases with your Lex V2 bot · Creating a version for your Lex V2 bot, final paragraph · Checked 2026-10-02
59. 59
    Wildcard Lex session attributes set in one Get customer input block apply across bots but not to other Get customer input blocks in the same flow.

    Flow block in Connect Customer: Get customer input · Additional configuration tips, wildcard bullet and Get_Account_Number example · Checked 2026-10-02

Documents

Cite this page

WarmTransfer. (2026, October 2). Troubleshooting Amazon Lex bots that misunderstand callers in Amazon Connect. WarmTransfer. https://warmtransfer.net/knowledge/amazon-connect-lex-troubleshooting

@misc{warmtransfer-amazon-connect-lex-troubleshooting,
  title  = {Troubleshooting Amazon Lex bots that misunderstand callers in Amazon Connect},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/amazon-connect-lex-troubleshooting},
  note   = {Verified 2026-10-02}
}