Coop connection

[DARKHEARTRETURNS]

so at the beginning, i tried coop got into a game, played for a little bit, was alright, now i was trying to play with a friend and for some reason, we can never seem to connect to one another and then the game gave me a NAT type 3 message although my ps4 shows NAT type 2 and all other games work fine, so i changed my router and put my ip into the dmz and opened and allowed upnp, my ps4 shows NAT 2 still but the NAT 3 message from the game is gone and i can connect to random people but invitations with friends never seem to work what else can i do ?!