If Everyone ever needs the answer this is what I did…
This plugin worked as an add-on to PMPro:
‘Paid Memberships Pro Network Site Helper’ https://www.paidmembershipspro.com/add-ons/plugins-on-github/pmpro-network-multisite-membership/
There is another one I tried ( Paid Memberships Pro Network Subsite Helper ) but it locks me out the whole time so i don’t recommend it.
Then people will have to pay when registering a sub site. (Clicking on the normal Register link).
BUT I noticed if someone entered a random sub domain that did not exist for example https://www.random.yoursite.com does not exist it takes a person to the Registration page without payment (Just enter your details and click ‘Gimme a site’).
So I added this code to my wp-config.php file:
define( 'NOBLOGREDIRECT', 'https://www.yoursite.com' );
So if someone enters a random sub doman site that does not exist it redirects you to the URL you specified. In my case it goes to the Home Page where a user can register from there using the paid option.
This will most probably work if you use sub directories as well instead of sub domains. Haven’t tested it yet.
