AWS Authentication Problem with POST/PUT but GET/DELETE work fine

I have a small set of API end points using AWS API Gateway & Lamda developed with the Serverless framework. All work fine from using the Serveless CLI tool Though Postman, I get this error with POST and PUT commands.

    "message": "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."

However, GET and DELETE commands work fine. I have the authentication set at Collection level so all 4 types of queries use the same authentication. It has to be that POST and PUT have a request body and the other two don’t. The requests must be getting assembled differently.

I saw one POSTMAN bug reported about a year ago with a similar issue trying to upload an attachment. It doesn’t look like that bug got fixed.

Anyone else able to connect to AWS API Gateway with API Key and Secret key?