When I use afterplay.io (my preferred emulator), it doesn't work.
That's unfortunate, sorry to hear that. For problems that only occur on emulators and not real hardware, I'll generally consider those to be bugs in the Emulator and will not address them. A better solution is for the given emulator having problems to improve the accuracy so they can run games without special accommodations.
The web emulator on this page is available as an alternative.
Use this one, works fine:
https://taisel.github.io/GameBoy-Online/
J = A
Z = B
ENTER = START
SHIFT = SELECT