PS4 resume a saved coop game

Hi guys ! new to the mudrunner here and need some help because I dont seem to be able to find a way to resume the coop game I started with my friend...I hosted a friends only game invited him then played for 1 hour but when we tried to resume, I cant find a way to invite him into the game. I can resume solo no problem or create another session but doing so will erase our progress. Anyone else having this problem ? is there a way around it ? thanks

selecting multiplayer, navigate to map from previous multiplayer session, select resume.

Your friends can join your session from the PlayStation party interface (outside of the game).

This session can be initiated by any previous multiplayer party member as the saved session is cached for each player, so.. a friend could resume the session and you could join it. The 'host' doesn't matter.

Game caches only one session, but don't save multiplayer games. If played anywhere else - your "coop" cache is lost. If you decide to join to your friend's cached game with your own lost - you will start at defaults but with saved progress from friend's game.