How to Add a Payment Method to Facebook Business Manager

Log in to Business Manager (https://business.facebook.com/settings) and go to the left-hand side menu.
Scroll down and select “billing and payment”.
On the left-hand side, select “payment methods”
Hit “Modify permissions” and set yourself as Finance Editor. (You might need to refresh the page after this step or skip this step if you don’t see it.).
Select the Grey “add” button next to “Add business payment method” towards the top center. (This is the card you want Facebook to bill).
Enter card information and click save