Did you find docs? I did a cursory glance around late last week and ended up just shrugging assuming that’s what I got for using Dendrite (positive)
Edit: Turns out, when running sliding-sync you really only need to patch the .well-known/matrix/client
configuration
Seems like you missed some things in your first read of the Mastodon thread. That might be why you’re not getting the response you’re expecting.