What works for me (and has been posted many many many times on many many many games over the last six years or so) is:
Make sure Overlay is off (there were issues with it crashing when first introduced and I don’t know if it’s been fixed yet)
Make sure you are running the current release (update) of the trainer and game.
Start the game (press play on Steam, then play on launcher, then close launcher once game is running).
ALT-TAB to WeMod and press play on trainer, once in game.
Use the trainer functions.
At least that’s what I have been doing in every game I use WeMod on since I started using the program (before I used the individual creators stand alone trainers). I NEVER start a game through WeMod.