I used AdSense on my Facebook App inside iFrames (which was the only way to do it back then in (2009->2010) I made around $2k to $4k monthly, got banned a couple of weeks before the payout cycle, I contacted them and filed two appeals, both were rejected and no reason was given besides that I wasn't complying with the rules, that was back in 2010'ish as I recall, right after Facebook forced the approved list of advertisers (Adsense wasn't in the list)