This article describes how to delete leads or customers from QuickBooks Online (QBO).  We're going to assume you uploaded some customers into QBO then deleted them.  When making your second attempt to upload those customers again you got an error message saying the customer/employee/vendor/othername could not be sent to QBO as the Name is already in use.

QBO never completely deletes a customer from their records - they simply list them inactive.

Resolution 

1. Open QBO and click the Clients tab. (depending on your settings in QBO, this may also be called Customers)
   
   
2. On the left hand side near the Import button, click the checkbox Show Deleted.  You should now see all the customers you thought were deleted.
   
   
3. Click any of the (deleted) customers then click the Restore button by the name.
   
   
4. Click edit beside the customer name and add "inactive" beside their Display Name As.
   
   
5. Repeat steps 3 and 4 for the rest of the customers you need to undelete.
   
   
6. Once you've finished preform a sync with Method.
   
   
7. After sync'ing go back to QBO and delete the customers again.
   
   
8. Preform another sync with Method.
   

Once the sync has finished Method will be clean of your deleted customers and QBO will have "inactive" beside all the customers names who shouldn't be there.  When you try to upload the customer again from Method you shouldn't receive any error message.