I have used Alipay, Kuaiqian and Tenpay to repay credit cards. I use debit cards from ABC and CCB, and I can also use credit cards from CCB, ICBC or China Merchants Bank. ICBC debit cards and China Merchants Bank credit cards are supported, and it is no problem to repay credit cards with Tenpay or Alipay balance. I think the problem may still be your CMB credit card. Fast money has a limit of 5 payments per month for credit card repayment of China Merchants Bank.