ah yes, another fork of BirdSiteLive. Every one seems to make their own fork of that thing. And none of them (that I've found) set a user agent when delivering messages to other AP servers.
You can see where bird.makeup sets the headers here[0] (with a distinct lack of user agent) and an issue I filed against the upstream[1] asking them to please set a user agent.
Have you looked at ChatSecure? It has OTR, multiple servers, all that good stuff. It's not wonderful but it ain't bad (curious to hear what others have to say, I haven't really used much else)
You can see where bird.makeup sets the headers here[0] (with a distinct lack of user agent) and an issue I filed against the upstream[1] asking them to please set a user agent.
[0] https://git.sr.ht/~cloutier/bird.makeup/tree/master/item/src...
[1] https://github.com/NicolasConstant/BirdsiteLive/issues/188