Support Alipay to repay China Merchants Bank credit card with ICBC debit card, and the repayment operation will arrive the next day. Alipay website itself is safe, as long as you log in from Alipay official website, don't click on other places to link to past pages (to prevent other third-party phishing websites).

I have used China Merchants Bank credit card to repay with Alipay for half a year, and I haven't encountered any problems.