Create and publish eBay inventory items and offers using the Sell Inventory API

Steps

1. Obtain an OAuth 2.0 user token with the sell.inventory scope using the Authorization Code flow; eBay Sell APIs require user-level consent
2. Create or replace an inventory item by issuing PUT to /sell/inventory/v1/inventory_item/{sku} with a JSON body containing product details (title, description, aspects, imageUrls), condition, and availability quantity
3. Create an offer by POSTing to /sell/inventory/v1/offer with inventoryItemGroupKey or sku, marketplaceId, format (FIXED_PRICE), pricingSummary, listingPolicies (fulfillmentPolicyId, paymentPolicyId, returnPolicyId), and categoryId
4. Publish the offer to make it live by POSTing to /sell/inventory/v1/offer/{offerId}/publish; the response returns a listingId
5. Update price or quantity by issuing PATCH or PUT to the inventory item or offer endpoint; quantity changes reflect immediately without republishing
6. Retrieve listing status and listingId via GET /sell/inventory/v1/offer/{offerId} to confirm publication and surface any listing errors in the warnings array