Why do you need to choose (or tell the worker) “credit” or “debit” when paying for something by card? Are the two cards built differently?

Question

Why do you need to choose (or tell the worker) “credit” or “debit” when paying for something by card? Are the two cards built differently?

In: Other

Answer 1

And why is this only in the US? In the UK we go to pay, tap our card / put it in and use the PIN, no clarification needed. The card itself is a debit card or a credit card, we don’t need to inform anyone ahead of time what we’re using.