I have a shader error on WebGL

When I build my modded FPS-Microgame project on WebGL, this error pops out:

Shader error in ‘Hidden/PostProcessing/Final Pass’: Input signature parameter (1- based Entry 3) type must be a scalar unit

And yes, I’m using Post-Processing in my Scene (Unity 2021.3.4f1 version)
This error comes while building the project and interrupts the build, but I still can play the game in Unity.
I cant code yet, so I didnt change anything in the scripts of the Microgame.
Its okay if you only tell me, what this error even means, so at least
I know what the problem is.

Plz help