Security error when calling external API via webhook

They refer to their cert as a 'wildcard cert'.   I did export the cert and when viewing it does give messages like "Windows does not have enough information to verify this certificate"    The endpoint I am trying to hit is a development system endpoint (not production).      The challenge is that if I take the same parameters and request json into another tool like Postman I am able to successfully make the call without doing anything related to the cert.