Authenticate with eBay's OAuth 2.0 user token flow with the https://api.ebay.com/oauth/api_scope/sell.inventory scope.
Call POST /sell/feed/v1/task with body {feedType: 'LMS_ADD_FIXED_PRICE_ITEM', schemaVersion: '1149'} to create a task and receive a taskId.
Prepare an XML file containing one or more AddFixedPriceItem objects — each must include Item.SKU, Item.Title, Item.PrimaryCategory.CategoryID, Item.StartPrice, Item.Quantity, Item.ListingDuration, Item.ConditionID, and Item.ShippingDetails.
Upload the XML file with a multipart POST to /sell/feed/v1/task/{taskId}/upload_file — the Content-Type must be multipart/form-data with the file part named 'file'.
Poll GET /sell/feed/v1/task/{taskId} until the status is 'COMPLETED' or 'COMPLETED_WITH_ERROR'; then call GET /sell/feed/v1/task/{taskId}/download_result_file to retrieve the processing report.
Parse the processing report XML — each result record contains a Correlation field matching your SKU, and a Code and ShortMessage indicating success or the specific validation failure.
Known gotchas
The LMS schemaVersion must match the version your XML feed uses — mismatches cause all records to fail with a schema validation error; check eBay's current supported schema version in the API docs before building your XML template.
LMS feed types require the item's CategoryID to be a valid leaf category for fixed-price listings — submitting a parent or invalid category ID causes a category-specific error code in the result file.
eBay item specifics (Item.ItemSpecifics) are increasingly required for listing approval, especially in categories like clothing, electronics, and automotive — missing required specifics result in listing suppression rather than upload failure.
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