Celtic Heroes

I spent 100 and trying to spend another 100 but it says error it can't go through or something? Anyone else?

Could be issue with bank rather than OTM, or maybe even App Store problem. Least likely to be a fault with OTM.
Check bank details are correct and maybe check for email from bank.

On my first purchase Google held the money for a while then it took a whole day of confusion until Google tells mr they finally sent the money to OTM. Google just randomly checks payments, I think, but I don't know why. I've been using the same debit apple with Play for three years.

CrAsHeD is correct.

Usually, when there is an issue on your account it means Apple / Google are doing verification checks or require you to contact them before proceeding.

If this is your first time using a new apple on the account, from personal experience, they lock it to verify the purchase was legit.