I am struggling to show data from custom fields in my Profit and Loss detail report.

Hello there, @wmansour-infomin. 

Welcome to Community. Allow me to share insights about the data not showing in the custom fields and help you from there. 

You can find Custom Field in the filter section when running Transaction List by Customer and Transaction List by Vendor. 

For additional resources, here's an article about customizing your reports in QuickBooks Online.

I'm adding these articles that will help you manage your custom fields and track the details that matter to most of you: 

• Filter, search, and sort with custom fields.
• Use custom fields in reports in QuickBooks Online Advanced.
• Use custom fields for vendors and expenses in QuickBooks Online Advanced.

Let me know in the comment section below if you have any other issues or concerns. I'm more than willing to help. Have a wonderful day!