How to run custom extension using PyAEDT code written across multiple scripts

I'm trying to develop a custom extension for Maxwell3D using PyAEDT. The code for the extension is divided into four scripts for organization purposes. I have no problems running the extension using the Run PyAEDT Script
button.
I installed the same custom extension via the Extension Manager. The installation seemed successful, and a new button which corresponds to my extension appeared beside the Extension Manager
button. However, when I run the installed extension I get the following error:
[error] Process 'run_pyaedt_toolkit_extension_name.cmd' run time error code 1, run by RunProgram script command.
I looked into it, and it seems I only get this error when my code is divided into several scripts. It happens even when I manipulate the PYTHONPATH
to add the folder containing my scripts. When everything is in one script, the installed extension works.
Am I missing something and is there a way to install and use an extension with PyAEDT code divided into multiple scripts?