Thank you for the quick response, @Marco_bau.

Let's go over to your sales transactions and make sure the correct income account is selected. 

Here's how: 

1. On the left pane, select Sales.
2. Click the All Sales tab. 
3. Select the Filter drop-down menu.
4. From the Type drop-down menu, choose your desired transaction type and date.
5. Hit Apply.
6. Select the transaction.
7. Click More and select Transaction journal.
8. Check the posting account if it's an income account. 

If the account is incorrect, you need to change the account for that product/service item. If it's the right income account, it's possible the data entered is damaged. To fix this, you can delete and recreate the transaction in QuickBooks. 

Please know that I'm just a post away if you have any other questions. I'll be happy to help you out. Have a great day.