Basically the below online betting/gambling sites used to have a promotion where when you join you get £10/£5 free to spend betting (one gives £10 the other gives £5).
Both sites made the same mistake, they didn't make the "free money" only available to be used for playing games, you can actually withdraw this free money!
You can do this as many times as you want as long as you use the exact same link (if you join via another link it will go to the normal site, where you get the free money but the mistake is fixed and you can't withdraw it, with this link you can withdraw it!) as long as you use a different credit card number each time!
Here are the links:
This one is for free £10, you deposit £10, get £10 free, withdraw £20 (£10 profit):
--link removed--
This one is for free £5, you deposit £5, get £5 free, withdraw £10 (£5 profit):
--link removed--
They both redirect you to the promotional page with the loophole, remember to use these exact links!
I've made £100 from this, using different cards!

