You cannot directly buy Meta (Facebook) ad credits as a product. Instead, you can either to your account or claim promotional credits issued by Meta or its partners. 1. Adding Prepaid Funds (Purchasing Spend)
If you want to "buy" balance for your ads ahead of time to strictly control your budget, you can add prepaid funds: buy facebook ad credits
Claim a Meta Ad Credit | Meta Business Help Center - Facebook You cannot directly buy Meta (Facebook) ad credits