wss://relay.mostr.pub and wss://ditto.pub/relay
Discussion
Here's the answer that helped me in the past (thanks to looking through my backup file)
Just a quick update. I’ve been doing some testing and I noticed that I’m getting ActivityPub content from both wss://relay.nostr.band and wss://ditto.pub/relay too.
Oh, that’s right. I saw both on https://mostr.pub but only wss://relay.mostr.pub makes the bridge. 