Friends are only permitted in Dead Island 2 if you have a PS5 or Xbox Series X

Those playing Dead Island 2 on last-gen consoles will be sorely disappointed as they cannot host multiplayer sessions. 

Dambuster Studios has thrown a spanner in the works for those gearing up to play Dead Island 2 on their PS4 or Xbox One. Thanks to restrictions caused by the zombie shooter’s graphic requirements, only those with more recent consoles will be able to host two or more players on their server.

Source: www.techradar.com