Imported module in Android Studio can't find imported class

First of all, you must import your library project by following that path:

File --> New --> Import Module

After you have imported the library project successfully, you must check your build.gradle file inside your project's folder if the following line is present at the "dependencies" section:

implementation project(':NameOfTheLibProject')

Then your project must be built successfully.

I found that my issue was the Android Plugin Version under Project Structure --> Project was different to the version my plugins all used. Once I aligned them to the same version, I could see all my classes from my imported module.

Took me hours :(

I had the same problem. I just did: Invalidate / Restart ..