Unable to join online DD game, no game pass ultimate

[wizardinthecorn_XBL]

I have Xbox game pass ultimate and have installed the xbox one x|s version of the game. I have a friend who has Xbox Live Gold, he purchased the xbox one x|s version. He is unable to join my Diamond Dynasty co-op, he gets a message saying he needs to upgrade to game pass ultimate.
Why is this the case, we both have the same versions of the game installed, and both have xbox live gold. Seems broken that game pass players can only play with other game pass members.