The UPS REST ship request wrapped the reference as
{'Value': [{'Code':'BM','Value': picking.name}]}, but _ups_rest_prepare_shipping_data
already builds reference_number as a list of {Code, Value} dicts. UPS expects
ReferenceNumber to be such an object (or array) with a STRING Value and rejects
the double-wrapped form on the ship call. This branch fires for every non-US/US
(e.g. CA->CA, CA->US) shipment, so rating worked but label creation failed.
Pass the list directly. Validated end-to-end against UPS production from a
Canadian origin: rate + real label (tracking 1Z6W...6355, then voided).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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