If you have a reference number on a FedEx Return label that is longer than 19 characters, you see:
Error: Reference number cannot be longer than 19 characters
When processing a return label for a Sales Receipt or Invoice, QuickBooks Shipping Manager automatically populates the Reference Number field on the label with "Sales Receipt #" or “Invoice #” where # equals the Sales Receipt or Invoice number in QuickBooks.
When the Sales Receipt number is more than 5 characters (or more than 13 on invoices), the length of the field data exceeds the 19-character limit.
To correct this issue, manually edit the reference number to be 19 characters or less in Shipping Manager.