UPS International Shipment > Getting error: 'Package level reference numbers are not allowed for UPS shipments whose origin/destination pair is not US/US or Puerto Rico/Puerto Rico…'

Problem/Business Requirement/Unique Question:  

When using UPS to ship internationally, the pop-up error message below is being returned:

'Package level reference numbers are not allowed for UPS shipments whose origin/destination pair is not US/US or Puerto Rico/Puerto Rico.
If you enter data in the Reference #1 or Reference #2 fields for shipments that do not meet this requirement, the data will be saved locally but will not appear on the UPS shipping label.'

Solution/Workaround/Gotcha/Recommendation Details:

If you are shipping internationally using UPS, the values entered under the Reference #1 and Reference #2 fields under the Packages tab of the Item Fulfillment will not be displayed on the Shipping Label.

The package level reference data is not allowed by UPS on International Shipments. Data on those fields will be ignored and only the sales order number will be submitted. This applies to all packages in the shipment.