Adds a batch of coupon codes to the available pool of a unique-code variant. Requires a producer access token for the application.

Send up to 5,000 codes per request, each up to 255 characters. A code already on this variant is skipped, not treated as an error, and the response reports how many were accepted and how many skipped. A code already used on a different variant in the same store fails the whole request, so a bad file never takes over another variant's codes.

The variant must belong to a unique_code product, and the product must not be published. To replace the pool instead of adding to it, use Replace Coupon Codes.