Security error when calling external API via webhook

A wildcart cert is fine. If it is dev, it is possible they are using a self-signed certificate rather than coming from a trusted authority, which Quick Base will not be able to validate. It works fine from your local PC via Postman because there is no additional security check occurring there. If you run the domain against SSL Labs, what is the result? If you aren't comfortable sharing the domain publicly, let me know and I'll reach out to you via email (I found the case).