Your Cost Code in SynkedUP is most likely linked to a "Category" instead of a "Service" in QuickBooks Online. QuickBooks does not allow creating invoices with Categories, they only allow Services.
How to Fix a Cost Code Linking Error
1. If you get this error message follow the steps below to resolve.
2. Click "Plan"
3. Click "Edit"
4. Verify which Cost Code is causing the problem.
5. Click "Setup"
6. Click "System Setup"
7. Click "Cost Codes"
8. Click here to edit the Cost Code in question.
9. Click "Hardscape"
10. Verify that there are two with the same name.
11. Open your QuickBooks account and navigate to "Products and Services"
12. Find the corresponding Service and Click "Edit"
13. Click the "Category" field.
14. Rename the Category with something different than the service.
15. Click "Save"
16. Click "Save"
17. Switch to tab SynkedUP - Setup"
18. Click this icon.
19. Click this icon.
20. Click "Link to QuickBooks"
21. Link the Cost Code to the correct Service.
22. Click "OK"
23. Click here to save
24. Click "Create New Invoice"
25. Click "Create Invoice"
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