I'm trying to build an app, and a trivial part of the app is creating and joining "groups", as in chat groups. The first part is working well, any user can create groups and they get stored as a collection in firestore firebase. The second part isn't working at all, no other user is able to join a group with the generated 6 digit alphanumeric code. I keep getting the same error : "firebase has missing or insufficient permissions". Could anyone help me define the rules for my specific case?