Apple Pay for repairs?

In an Apple Store? Probably, assuming you're not planning to use the device that currently needs repairing. Depending on what you're having fixed you may get a refurbished device rather than your original. It may also depend on what maximum spends are allowed on Apple Pay where you are.

tt2

Yes you can, all Apple Stores accept Apple Pay both for new products and repairs with no spent limit. (As someone as already said though, you'll need a device different from the one being repaired.)