Quickbooks Error Code (620): TxnID cannot be linked
For a full list of Quickbooks Error Codes that you might encounter, click here.
For more information on how you can find Quickbooks errors in your account, click here.
An invoice / sales receipt record with this number already exists in QuickBooks.
Additionally, this invoice / sales receipt in QuickBooks exists under a different customer than the customer for the Bill in Syngency is mapped to in QuickBooks.
This almost always means that the existing invoice / sales receipt record in QuickBooks is a totally different/unrelated record.
Revert any changes made to the Matter Client in Syngency, if it's been modified since the Bill was synced over to Quickbooks.
Change the Invoice ID to be unique, and re-sync.
If that doesn't work, you may need to re-generate the Bill to force the re-sync (with a new Transaction ID.)