can not play PvZ garden warfare on PS4 sub accounts why not?

My son is the primary on the ps4 (he is 18). And a plus member. I got pvz 2. I am not a plus member. I was able to play online on my account until tonight. I froze during an online match. When I reset and went to join an online game it stated that I had to be a plus member. So I tried another online game and was able to play online. So I put PVZ2 back in and got the same message. Curious as to why I could play before but not now. Does this mean I have to pay for plus for myself and my son? I hope not!