Call to undefined function error in my extension

The extension I’m writing is fairly simple structurally. I have a main method called do_geo() which at one point calls another function called myWithin(). However, I keep getting this error…

Edit: this seems odd as well. The error message:

Call to undefined function mywithin()...

shows the function name as all lowercase, but the actual function is called myWithin, and the call to it is correct…