Cannot get anything other than "The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details." when sending from ReadyAPI.
Using the same request and AWS IAM credentials in Postman allows messages to be posted to the queue.
The only difference I can see is that in the headers, ReadyAPI adds x-amz-content-sha256 to the header, whereas Postman (which works) does not create or add this.
Both are sending the Authorization header as below