When I checked Profit and Loss by Customer, I found that my supplier is included in the report. Even though I didn't add that supplier to the customer list

I'm here to share to you some information about the report and guide you on what to do, aini-asiacommerc,

Are you referring to the Profit and Loss by Class report? Normally, the information you see from the Not Specified column are those transactions that doesn't have a customer or Class assignment. You'll have to make sure to add your customers correctly so it would show the correct details on the report. To add your customer as new class, follow the steps below:

1. Click the  Gear ⚙ icon and select All Lists.
2. Select Classes.
3. Select New. Give this class a name.
4. To add a sub-class, select Is a sub-class and select the main class. You can nest up to five classes.
5. Select Save.

Furthermore, QuickBooks Online (QBO) provides different kinds of reports that caters your business needs. Learn from this article on how to customize them so you'll be able to get the information you need: Customise Reports In QuickBooks Online.

Reach out to us if there's anything else that you need about reports. We're always right here to help you all the time.