Getting the 'CertPathValidatorException: Certificate chaining error' when running through my Instance (see attachment). I get results and no errors in Postman or running through a web browser. I saw some previous posts on installing trust cert in Breeze. We don't use 3rd party certs for SMGR so I installed the SMGR trust cert into Breeze but made no difference.
I've had success with some other API workflows although this one is HTTPS rather than HTTP. I will admit certs are not an area I am overly familiar with so I wouldn't doubt something may still be missing.

You need to install the cert, from the api/https service that you are calling, on the breeze cluster. Open the https url in a browser and then download the cert to your hard drive. Take that cert and install it on the Breeze cluster (breeze cluster administration - certificate management drop down).