Can't add more than 3 players

Several of us have the starter sub. I've been trying to start a campaign. But it refuses to let us add a fourth person saying in the campaign is full. According to the ad: the starter pack should allow you to have at least four players.

All four of us have tried using multiple different worlds, reach of us have tried hosting and all of us have tried sending invites, but it always comes up the same.The fourth person always gets excluded for the message saying the campaign is full.

All of us have paid starter tiers.

We paid for these accounts specifically so other can play, but now we are feeling a bit ripped off.