The max_id, since_id, and min_id parameters in #Mastodon's Timeline API assume that the post ID is a sortable number. (Is this correct?) #Hollo, the #ActivityPub implementation I'm building, uses UUIDs for post IDs internally, so I'm stuck on how to implement a Mastodon-compatible API.
I actually started #Fedify because I was working on a single-user #ActivityPub implementation called #Hollo and felt like I needed some groundwork, and now that I'm somewhat done yak shaving, I'm back to working on Hollo, although I still jump back and forth between Hollo development and Fedify when I think of features I need for Fedify.
The fedify inbox command, which will be shipped in the next #Fedify release, is a tool that creates an ephemeral #ActivityPub server so that you can debug and test the activities you send.