Been integrating with a third party system for the last 2 weeks, we can send them requests fine but when they post the response to us they get a generic error.

After responding very politely to an increasingly aggressive contact at their company for the entire day, where he says it is our system that is badly configured, they figured it out.

Their system only has support for sending data using TLS 1.0 and below....

So turns out he was right our system wasn't configured to work with theirs. We only allow 1.2 and above...