Compare the invoice in Kennel Connection to the invoice in QB. Modify the invoice in QB so that it matches the invoice in KC. The receipt will then transfer.
If this does not work, you can also try deleting the invoice in QB, finding the invoice in Accounting, Invoices in KC and marking the invoice as "Not Synced" by double-clicking on the QBDL field to the right. Then, try syncing again.