incentive@mastodon.circlewithadot.net The code suggests that when parsing the follow request, it's checking object and ensuring that it is one of:
https://www.w3.org/ns/activitystreams#Public
It's own ID (so, https://relay-us-east.circlewithadot.net/actor)
NodeBB is sending https://relay-us-east.circlewithadot.net/actor, so it should satisfy that constraint, but I am not sure where in the Activity-Relay code it is failing out.