No as the trace stack\error handling in the API is not being very descriptive.
On face value, as other requests are working, and its also running in ReadyAPI, then it would appear to be something wrong with the request.
You are missing an element or header, or something similar.
As the error handling is not very descriptive, then my initial recommendation is to investigate the raw body in ReadyAPI and compare that with the console logs in Postman.
My further recommendation is to to discuss this with a DEV or the supplier of the API that you are trying to consume. Hopefully they will be able to add more on what that error actually means.