7 days to join the not working?

Moin, me and my amigo try to play the game together but if I go into a private game and try to invite him, he always gets an error message, the other way around, there were rare cases where it worked maybe 1/100 times your ideas why? (play on the xbox one)

Normal. There's a trick, but it doesn't have to work.

Both hold down the xbox button on the xbox for a long time until it goes off. That should clear the cache.

Then just restart and go straight into the game and invite.

It always worked for me and my buddy at the time.

At best both LAN and NAT open