How to add Master Card to Promote Page or
Boost Post in Facebook (ios app)
Login into your Facebook account and choose More button
Choose Pages
Choose a page you want to promote
Choose More
Choose Manage Adverts
Choose Create advert
Choose a page you want to promote
Choose desired option (Promote website, Promote page, Boost post)
Scroll down and sep up details
Set up audience, locations, interests
Set up your budget
Choose Add Payment Method
Set the country Cambodia and choose New credit or debit card
Fill your card details (Card number, expiration date, CVV) and press Save button
Here is an example:
Choose Promote Page

You can get free Virtual MasterCard following instruction