My game keeps crashing when trying to start up with this mod installed. When I take it out it starts up like normal. Below is the error message I get:

The game crashed whilst initializing game
Error: java.lang.RuntimeException: Could not execute entrypoint stage 'main' due to errors, provided by 'simple_backpack'!
Exit Code: -1

Are you using the required Cloth Config API mod as well?

I thought I did, but apparently I downloaded the forge version instead. Sorry for the bother, I'm still new to modded minecraft and getting used to the fact that there's 2 mod loaders and thus different files.
It works perfectly fine now 😄

Glad it was a simple fix. enjoy.