Apologies for not being clear enough, just edited my message here.
I’m having trouble using Mercury Messenger 4.0.2 on Android 8 & 6.
No matter what server I change it to, it doesn’t work. Now my friend
can’t message me as it’s all of a sudden stopped working
No, I have not a older version of Mercury Messenger, in this moment I use the most recently version and it work fine with other protocol different of MSNP21, for example the protocol MSNP15, the only way Mercury Messenger worked on my phone with the version 4.0.2, sorry I can’t help you, I think it’s a bug in the app, since it’s still in beta phase yet.
You can report the error with Escargot team, probably they help with problem,