Why “USED” Condition Fails in eBay Inventory API (Action Figure Category)

curl -X PUT 'https://api.ebay.com/sell/inventory/v1/inventory_item/test-sku-001' \
  -H "Authorization: Bearer DUMMY_ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "condition": "USED",
    "product": {
      "title": "Dummy Action Figure",
      "description": "Dummy description for an action figure item.",
      "imageUrls": ["https://dummyurl.com/dummy-image.jpg"]
    },
    "availability": {
      "shipToLocationAvailability": {
        "quantity": 1
      }
    }
  }'
\```
{% endraw %}


### Error Response

\
{% raw %}
```json
{
  "errors": [
    {
      "message": "Could not serialize field [condition]"
    }
  ]
}
\```
{% endraw %}


## ✅ Example: Success with {% raw %}`"USED_EXCELLENT"`

\
{% raw %}
```bash
curl -X PUT 'https://api.ebay.com/sell/inventory/v1/inventory_item/test-sku-001' \
  -H "Authorization: Bearer DUMMY_ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "condition": "USED_EXCELLENT",
    "product": {
      "title": "Dummy Action Figure",
      "description": "Dummy description for an action figure item.",
      "imageUrls": ["https://dummyurl.com/dummy-image.jpg"]
    },
    "availability": {
      "shipToLocationAvailability": {
        "quantity": 1
      }
    }
  }'
\```
{% endraw %}


Now the **USED** listing works correctly via API.

## Summary

- In the Action Figure category (and similar), the **UI only shows "New" and "Used"**, but...
- The eBay Inventory API **does not accept {% raw %}`"USED"`{% endraw %}**.
- Instead, use {% raw %}`"USED_EXCELLENT"`{% endraw %} (Condition ID {% raw %}`3000`{% endraw %}) when listing as used.
- Therefore:
  - New item → {% raw %}`"condition": "NEW"`{% endraw %}
  - Used item → {% raw %}`"condition": "USED_EXCELLENT"`{% endraw %}
- This mismatch stems from eBay’s internal {% raw %}`ConditionEnum`{% endraw %} design and is **not clearly documented**, making it a common source of confusion for developers.