Create a subscription button:
https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/subscribe_step_...
Export it as button or as a link to add it to your Facebook page depending if Facebook let's you add html on your page.
If you have to export as a link instead of the button code, you can link it with a donate button image url via html using the donate image urls from here:
https://developer.paypal.com/docs/classic/api/buttons/
Kudos & Solved are greatly appreciated. 🙂
