So I just got the game and my friend can't join me on his higher level character but he can join me on a lower level character
Is there a leve restriction or something ?

there is a level restriction unless you're using a password to play together

we are using a password

try waiting a bit longer or try a more obscure spot perhaps?

From what I know lower chars can summon any char as long as its in their world for instant if your friend who is higher level will try to summon you it wont work as you can only scale down and not up so he will be scaled down to your world but you cannot scale up to his world

When there's a large lvl gap between the players joinin a password in game it takes a bit longer for the sign to show up.

it seems to work fine now
i looked up a few things and looks like its just in early areas?

it seems to take a while to matchmake with high lvls in some areas