My created paid subscription doesn't work :(

[Goodman_2020]

I tried to create a piad subscription, i did it without problems. But i tried it, and it doesn't do anything.
There's the normal usergroup "registered users" they have the right to create threads, answer threads, post messages etc. well more or less they can do all EXECPT one thing... i disable the possibility to use the private messages, setting the capacity of the box to "0" (someobyd told me it wil ldisable it, and it seems)

Then i created a new public usergroup that we can join. It has exactly the same permissions as "registered users" except that they have the possibility to use the private messages. For that, for them i set the inbox to 50 messages

Then i created a paid subscription, and i chosed that "registered users" go in "premium members"(the name of the new additional usergroup) once the subscription is paid.
I let the forum access on the same page to "default".

Then i created a fake member etc. and a fake cost (1?) to test the transaction. I tried it, and the payment works fine, no problem with that.
The subscription appears "active" in the menu.
But no trace of the private message system, it seems that i'm still a simple registered user.

So i wonder what i did wrong, somebody can help me please?

Thanks