Hi @gro1900,

Usually this happens when one of you is on an IPv6 address and trying to matchmake with an IPv4 connection.

If this is the issue the best way to resolve it is to set a Static IP address to your console and then DMZ it (Note: Please do NOT DMZ your PC IP Address). If the issue still occurs after DMZing your co-op partner will most likely need to follow the steps as well.