error: No usable messages given the current slot and sessionAttribute set

Question

I made a chatbot in lex and for one particular intent, Lex is throwing the error,

An error has occurred: Invalid Bot Configuration: No usable messages 
given the current slot and sessionAttribute set.

This error comes regardless of the input in case of that intent. I am not using any lambda functions at this point for this intent. Can someone guide me what this means? I am new to lex and I did not find references to what this error is about.

Answer 1

Recently I got the same error with the test of my bot after saving some changes. After a while, finally, I found out that it was because my confirmation message was using some slots not defined at that point.

Example:

Let's assume we have:

• one required slot {name}
• one optional slot {age}
• and the confirmation message is "Your name is {name} and your age is {age}, is that right?"

If Lex reaches the point to ask for the user confirmation and {age} was never assigned whether in any utterance or a lambda function, then Lex will return this error.

You must ensure that all slots used in messages are defined.

Answer 2

I believe this error occurs because you have not configured Lex to have a response message set for that particular intent's CodeHook or Fulfillment.

If you are not using a Lambda Function for Fulfillment, be sure to select 'Return Parameters to Client' in the 'Fulfillment' section, then also supply a response message below that in 'Response' section.
Here's where to find that in the Lex Console: