This happened to a friend of mine recently, so we basically just stumbled on a way to get a free Facebook ad credit. What you want to do is log into your Facebook advertising account (I assume it only works with a new account you haven’t used before) and create an ad for pretty much anything you want. Continue with creating the ad until you get to the point where you “fund” the account with your credit card. At this point, just stop and close the page or log out.
In a few days, Facebook Ads will send you an email mentioning that they noticed you didn’t finish setting up your ad and in that same email they will offer you a $50 coupon for an ad credit. Pretty simple. Post in the comments below if you have any success with this!