how do i write a custom report that provides a detailed P&L?

The option to generate and create a detailed Profit and Loss report in QuickBooks Online depends on your subscription plan. Allow me to explain this further, Junction.

The Profit and Loss Detail report is available exclusively in QuickBooks Essentials, Plus, and Advanced versions. If you're using these plans, you can easily access this report by navigating to the Reports menu.
 

Afterward, customize it to show more details and save it. Please see the attached screenshot for visual reference.

If you're using the Simple Start version, consider upgrading your subscription to create and customize detailed Profit and Loss reports.

Here are the steps to follow:

1. Go to the Gear icon, then click Subscriptions and Billing. 
2. Hit Upgrade your plan in the Billed to You section.

Once you've upgraded, please follow the steps above on how to generate the detailed report.

This thread will remain open for further queries. We're always here to help.

Hi @junction81,

I just wanted to follow up to check if the resolution we provided helped resolve your issue.

Please let us know if everything is now working as expected or if you're still experiencing any problems.

We'll be glad to assist further if needed.