Integrate pay Wall to existing wordpress website

To access the forum at [login to view URL] there should be integrated a paywall. Users should have access for 30 minutes if they pay €19,-. After the 30 minutes. They should pay €19,- for every other time they want to be 30 minutes on the forum. Users should pay with IDeal. Current situation : after registration people pay €19,- via IDeal and have unlimited access.