Issues uploading to url provided by /attachment/upload

Is anyone successfully using the Upload URL provided by the /attachment/upload to upload an attachment.

Currently trying to use it but continually getting an SSL error which appears to be like SSLError: SSL validation failed … EOF occurred in violation of protocol · Issue #3359 · boto/boto3 · GitHub (albeit I am using Python directly)

This suggests a setup issue on the AWS end but of course that is out of my control.