My friend bought the game and played but now the new update is out so... he tries to login so he can update the game but it does not recognize his email so he cannot login or get the game. Basically he paid for version 1.4 and that's it.
Human! You are about to become a sword robot! · By
I dont know if this helps but.
https://doborog.itch.io/clonedroneinthedangerzone
Click on buy now. then on "i already paid for this"
Then a website should open, there should be a textbox asking you for the email. Tell your friend to enter your email and it should be mailed to him.
Obviusly this is a temporary solution, but i hope he can get it fixed!
Goodluck
-Teewoo
EDIT: Or your friend never made an account. But bought the game with his Paypal email, he should make an account and link his purchase to that account!