What is the ruling on using a credit card or "buy now, pay later" schemes?

Using them for convenience and paying in full before the due date without incurring interest is not prohibited; the problem is paying riba interest and borrowing beyond one's means.
Allah forbids riba and gives a stern warning to those who persist in it (al-Baqarah 2:275–279). Conventional credit cards charge interest on outstanding balances, while credit card-i products use Shariah contracts; pay-later schemes usually impose late charges. For family finances, the greatest danger is impulsive spending that piles up: the Prophet ﷺ often sought refuge from debt because a person in debt easily lies and breaks promises (Sahih al-Bukhari 2397). Guidelines: one card only, a low limit, pay in full every month, and do not use it for daily needs you cannot afford in cash. If you are already trapped, get help from AKPK. See Family finances.