Unable to validate sigv4 signature

My question:
I am trying to integrate with sigv4 and I am able to successfully validate with a GET request, but I am unable to successfully validate with a POST request. My assumption is that the request body hash is calculated differently between postman and my application. I would like to be able to debug through the postman code to be able to see how the signature is created. Is there anyway to do this?

I’ve already tried:
I have a test created application side based on the Postman data sent to the app, but without more context of how the signature is created on Postmans side its not very helpful.