To decouple (unsync) a synced invoice or expense from your accounting package:
In Halaxy, navigate to the invoice or expense and click Xero, QuickBooks or Reckon in the top-right.
Click the Unlink icon next to the line you wish to unsync.
RESULT: The invoice/expense is no longer linked between Halaxy and your accounting package, and further updates to the invoice/expense in Halaxy will not be synced. You can re-establish the sync, or sync it to a different invoice/expense in your accounting package, by manually syncing.