For what it’s worth, I’m a native British English speaker and don’t instinctively consider “practice” “grammatically incorrect”. Indeed, I would probably write “practice” myself.

Pretty sure I had this corrected on more than one occasion when I was at school. Also licence/license. I remember one day figuring out the parallel with advice/advise as a way to remember which was which. So C for the noun and S for the verb.

Weirdly (to my brain), Americans always spell practice with a C, but always spell license with an S.

That's why you need a good spellchecker.