I lost €4k in a Facebook scam
As someone who's fairly involved with the e-commerce/digital marketing space, let me just say I'm amazed by how brazenly nasty this scam is.The TikTok promotional program is actually a real thing that does give around that amount of ad credit, and they have been promoting it very aggressively on Facebook with for a long while now, so it makes sense that OP would've not had any mental red flags triggered by the designs and creatives used by the scammers. The real killer is that PayPal is actually well within their rights to process this transaction (as part of the billing agreement generated when you link PayPal to Facebook Ads Manager: there actually was real ad spend in a real Facebook ad auction), so it's down to Facebook itself to refund the ad spend. (As an aside, I'm actually impressed that OP managed to reach Facebook support at all, and that they acknowledged or even understood what the problem was. I have had worse experiences in the past with FB...). What's really amazing to me is that the scammers managed to get on Google Play with thousands of obviously fake reviews, and get through Facebook ad review at all.The scammer silently removing OP as an admin from their own ad account, preventing them from noticing or stopping the fraudulent ad campaign is just icing.I suppose the real lesson to be learned is to simply avoid installing native applications when you can help it. OP didn't screenshot the login screen in app, so I can only assume it was a real Facebook oauth flow, but honestly at that point it's already too late. If anything OP should be grateful that the native app running on what was presumably  his personal device didn't do anything worse.