I’m US based and always use credit cards online (and pay them off every month of course) for the strong consumer protections they offer vs debit: $0 fraud liability, extended warranties, and rewards points/travel miles.

I’m curious about your experience here: have you ever encountered a scenario where you wanted to use your debit card, but the merchant only accepted credit cards?

Oh sure, debit vs credit is largely a non-distinction here since debit cards are generally on the same network: Visa or less commonly MasterCard. So unless there are other business-related reasons to deny debit cards (currency conversion or cross-border regulations maybe?), they should be handled by the same processor as a credit card and usually for a much lower transaction fee too!