This happen to me as well. Anyway to reverse this charge?
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The 21 tokens is from Facebook! Not a scam.
It is for registering a payment method for the first time, doesn't have to be credit card. You can use paypal too.
The 1$ transaction is just to make sure the account is functional, and gets refunded back usually within 24 hours. (other businesses do this too, it is a standard practice)