Process Details page: message "BASE APPLICATION CODE CANNOT BE VIEWERD FROM AN EXTENSION"

Summary:

I would like to customize the Process Flow Process-details page but cannot switch to the 'Code' function, although Live and Design are enabled.

Content (please ensure you mask any confidential information):

The tooltip message "BASE APPLICATION CODE CANNOT BE VIEWERD FROM AN EXTENSION" is displayed when I hover over the disabled 'Code' button.

Is this a permission issue?

Version (include the version you are using, if applicable):

Fusion Payroll 25D

Code Snippet (add any code snippets that support your topic, if applicable):