Since you specifically asked for feedback:
Multiple projects, the same account: host all of your firmware in up to 16 separate CI/CD projects.
This seems to imply that you're
providing CI/CD... but that doesn't seem to be the case from what I see (unless I missed something) you just have an API that can support working with an external system. It might be good to clarify/reword that.
Free, and open-source software matters to me
Oh, ok, so where's the source?

Or, in a slightly less snarky tone: this seems like it might be a useful convenience, and I'd consider paying for the convenience of someone running a service for me if I wasn't locked into it and had the option to run it myself. I'm extremely unlikely, however, to subscribe to something that's a closed platform charging me for the ability to use hardware I already own. I'm far from a FOSS zealot and pay for plenty of software. However I consider dev tools in particular one of those places that I rarely compromise... either they need to be open source, or they need to provide some form of offline perpetual license that doesn't rely on the vendor, so that my process isn't similarly dependent.
Please check out our community Discord server
I find discord particularly non-conducive to actually building a useful community, and generally don't use it unless forced to. Chat can be a nice adjunct to some more persistent format, but is a rather poor primary format and isn't really necessary. And if you do offer chat, just please,
anything but discord.
Also, I find it hard to read the API docs with the body payloads only specified by
-d params to curl... better to have an explicit payload specification. (and better yet to just accept json rather than form encoded.)