HI all, I’m experiencing the same issue on PikaPods and hoping someone can help me out 
I started setup of the site with their auto-generated DNS name, and when using that DNS name ActivityPub worked just fine. However when I switched the domain name to the one I actually want to use ActivityPub (and the network admin page) broke.
I’ve tried all the steps on this great writeup Fixing Ghost ActivityPub 404 Error on Self-Hosted Installation for testing and the it breaks down on the curl for .well-known/webfinger. The curl for the jwks.json works as expected (I think). The curl for webfinger returns a 403.
In the Ghost logs I see these two lines:
[2025-11-21 06:11:37] ERROR Could not get webhook secret for ActivityPub FetchError: invalid json response body at https://www.kentcountyindivisible.org/.ghost/activitypub/v1/site reason: Unexpected token 'i', "insert int"... is not valid JSON
[2025-11-21 06:11:37] ERROR No webhook secret found - cannot initialise
I have tried toggling ActivityPub off and on, both with restarts and without, I’ve tried restarting.
I’m currently wondering if it has something to do with changing the domain name after configuring it and navigating around the Network admin page.
I have emailed PikaPods support, who has said that everything looks fine on their end and encouraged me to ask here.
Thanks!