Is it possible to write Swift Code to Call Amazon Product Advertising API

I read in some very old posts that you need to get permission. I am trying to write something for myself on my Macbook using Cocoa Framework. I just want to retrieve data from Amazon Product Advertising API. The error message says:

"{"__type":"com.amazon.paapi5#InvalidSignatureException","Errors":[{"Code":"InvalidSignature","Message":"The request has not been correctly signed. If you are using an AWS SDK, requests are signed for you automatically; otherwise, go to https://webservices.amazon.com/paapi5/documentation/sending-request.html#signing."

But I checked all my parameters and signing method. I can share code but before that I am not sure if I am even allowed to do this using this client. (My credentials work in Scratchpad)