televisit-demo sendMessage from lambda assumeRole error

the lambda is failing when trying to return the response from the lex bot

2023-04-15T02:49:28.972Z 0696baa3-3d05-49ad-9758-495f33defbdd INFO {
"message": "User: arn:aws:sts::xxxxxxxxxxx:assumed-role/chime-sdk-televisit-backend-LambdaKinesisRole-1OJU72XPACAFW/ChimeSDKTelevisitDemo-MessageModerator is not authorized to perform: sts:AssumeRole on resource: arn:aws:iam::xxxxxxxxxxxx:role/chime-sdk-televisit-backend-LambdaKinesisRole-1OJU72XPACAFW",
"code": "AccessDenied",
"time": "2023-04-15T02:49:28.972Z",
"requestId": "674469a9-db9f-4cf2-8ed8-7499a67805b5",
"statusCode": 403,
"retryable": false,
"retryDelay": 6.397304262170911
}

Start with the televisit-demo Lambda sendMessage flow and the IAM role named in the AccessDenied message; inspect how the Lex response is returned and how sts:AssumeRole is configured. Reproduce the failing request, and consider the issue done when the Lambda returns the Lex response without the reported 403.

Written by the indexing model from the issue text.