[Question] Synapse administration and othe Matrix related questions

Hi, I'm trying to set up a self hosted messenger and tried Synapse on a Yunohost server. As of now, I can't log into the admin interface as I'm getting a variety of "forbidden" and "not found" errors. I tried with the "synapse" user as well as with the Yunohost admin user to no avail. Does anybody have an idea what could be wrong?

Dendrite seems to be a common alternative and I could get it to work on my machine. I would want a bridge to Signal, though - is there a solution available? All bridges I could find where for Synapse.