How can I add users to my team without getting locked out of my account? How do I get more licenses?

I purchased the Meistertask Pro monthly subscription through my ios. I thought the Pro license included multiple team members? I sent an invite to someone to join my team and they accepted. I see them in my team, but now I have been locked out of using my account because it says I don't have enough licenses. First, is the Pro plan only for 1 user? Second, if I have to pay for additional licenses then how do I do that? When I try to change my plan it directs me to iTunes but it doesn't give me an optioin to add any users/licenses.