If you edited a .cht file on a Mac or a modern Windows text editor, it might have saved as UTF-8. GenPlusDroid, being an older codebase, may reject this. Open the .cht file in a proper text editor and with ANSI or ASCII encoding.
GenPlusDroid allows you to use cheat files effectively. Here is a step-by-step guide to using and managing them. 1. Activating the Cheat Menu and load your chosen Sega Genesis game.