Not Being Able To Buy Stuff

I had this happening to me before and they told me that it’s a temporary security hold on the account after a balance change (like Quest Cash being added).

There’s nothing you can manually fix. The hold typically clears on its own within a few hours (sometimes up to 24h). If it’s still blocked after that (as I saw that your post was a while ago), the only real next step is Meta Support, since they’re the only ones who can see or remove account-level security flags.