"Peter never plays."

Translation: पीटर कभी नहीं खेलता है।

[J.Compean]

how would it work so say "hamesha nahin" rather than "kabhi nahin"?

[vinay92]

I would take it to mean 'Peter doesn't play always', ie, he does something other than playing every now and then.

[LinguisticBoi]

Think of it as a logic statement.

Kabhi is logic statement meaning "sometimes" meaning "at least once"
the opposite would be never

[nog642]

Why is "पीटर कभी खेलता नहीं है" wrong?

[vinay92]

That is also correct. You can report if you see the sentence again.