@KS You're opening this link exactly? https://firstname.lastname@example.org
That'd be interesting. The CA is Let's Encrypt, which should be trusted by all browsers and servers by now. Could you show me details on the SSL error?
@KS Oh, haha, have a safe journey! Let me know when you have time and motivation.
What I've been able to find so far, through access logs, is that your instance is getting response served like it's a web browser. E.g., /@king redirects, instead of serving the JSON it should. So I'm wondering if the Accept header is not getting through? Looking at Mastodon code, it should work, also for the version you're running.