For me, contactless=Apple Pay enabled, really just depends on the age of the contactless reader.
Asking for "

Pay" seems to confuse quite a few , so I just ask if they do contactless.
If they say
"yes, si, oui, tak, نعم فعلا, ja or sim" (depending where in the UK I am

/jk) I treat it as an ordinary contactless payment - with my iPhone instead of a card - hold my iPhone at the contactless terminal, finger on the button, and 99% of the time it works. (Apart from a few Caffe Nero hold-outs).
Example: Bought a stack of books at Oxfam bookshop yesterday, the poor old dear ringing up the total had no clue even about contactless, I showed her which one I wanted her to use, and all fine.
For me, it has made payments one hell of a lot easier!
Now just get the loyalty cards on as well.