Hello @Silvano Paxia , Thanks for the question and using MS Q&A platform.
I am assuming that you are referring to "HTTP Error 403 Forbidden Messages:", please correct me if I am wrong.
To me still it looks like that request is reaching the API , otherwise it should had been a 404 error . I do not have all the details and I have not used Magento either , but I will start with checking logs on the Magento side and see if the request reached the API . Other simple thing which you can try (if not done yet ) is call the API using postman or curl and see if the request goes through.
Thanks Himanshu
Please accept as "Yes" if the answer provided is useful , so that you can help others in the community looking for remediation for similar issues.