About the Portfolio Project: E-Commerce Website category

Hi! I’m looking for some feedback on an error I keep getting when I try to run my app.
Here is my project’s repository.

I also posted my error question here and included relevant code.

My current error is about the register user route.
The error says: Route.post() requires a callback function but got a [object Undefined]

I have a feeling I have either a misspelling or a syntax error somewhere, but I’ve looked through all the files connected to that route multiple times and can’t seem to find it. Any feedback would be appreciated. Thank you!