It works!

Appearently you need to mention the remote category in the post (possibly also the title).

@testing-ground@community.nodebb.org Testing from another NodeBB server again again

@testing-ground@community.nodebb.org Hello World!

NodeBB Community (community.nodebb.org)

@samsapti@forum.fedi.dk Hi, Nice to see you!

@theflickx@community.nodebb.org I hear you in the other end too. It seems you have to mention a person with their full handle for the message to get through from here to there.

@malte@forum.fedi.dk Can I reply to myself so that this message gets through too?

@malte And if I reply to myself without the full handle? (Probably not)

@malte The EDIT didn't get through. Let's see if it doesn when I reply.

@theflickx@community.nodebb.org Good to see you too!