Partially update existing orders

Update specific fields of existing orders. Only fields present in the request payload will be modified. Omitted fields retain their existing values. Use explicit null to clear optional field values.

Note: The products and refunds fields currently cannot be patched. To modify products or refunds, re-submit the full order via POST.

Array fields (order_tags, discount_codes) are replaced entirely when present - no per-item merging is performed.

The entire batch fails if any order_id does not exist or any entry fails validation.