Error 21690 — Product identifier type required

Product identifier type is missing or invalid. Currently supported Product types are: 1) ISBN, and 2) UPC.

eBay's Item Specifics increasingly require product identifiers (UPC, ISBN, EPID, MPN, brand) for items in catalog-managed categories. Missing or invalid identifiers block the listing or limit visibility.

1. Look up the eBay Product ID (EPID) for your item using the FindProducts API — that's eBay's catalog ID.
2. If the product has a real GTIN (UPC/EAN/ISBN), submit it in the appropriate field.
3. If the product genuinely has no identifier (custom-made, vintage), submit 'Does Not Apply' (where allowed by the category).
4. Brand and MPN are required for many categories — fill both even if you only have one.

• Submitting 'Does Not Apply' in categories where eBay no longer accepts it — apply for a brand-specific exemption
• Reusing a single MPN across multiple variants — each variant needs its own