Hello Jill_Jill!
Yea, unfortunately, you are not allowed to sell items that obligates users to use a VPN in order to redeem the items. So all you have to do is specify the region in the listing and wait for a user that agrees and can redeem the item in that certain region.
In the case of others doing this type of forbidden activity, you inform us through reports or here in the forum and we will take the right measures toward that user.
God speed!
