Getting eBay to talk to Claude is not conceptually hard. It is an OAuth app, four values, and a permission list. The difficulty is that eBay names those values differently from every other marketplace, and one field asks for something that looks exactly like a URL but is not one.
The four values, and what eBay calls them
App ID is the client ID. Cert ID is the client secret. Both are in the eBay Developer Portal under My Account → Application Keys, and both are plain copy-paste.
RuName is the one that stalls people, and it gets its own section below.
Marketplace ID picks which eBay site you are operating on, and it has to match a locale that marketplace supports. This is mostly obvious — until it is not. eBay specifies en-US for Malaysia and Singapore, which is exactly the kind of detail you discover from an error rather than from a guide.
RuName is a name, not an address
In the developer portal you go to Keyset → User Tokens → Get a Token via Your Application, and you create or open a Redirect URL entry. In that entry you set “Your auth accepted URL” to the callback address of whichever client you are connecting. Orkas uses https://orkas.ai/api/connectors/oauth/dcr-callback, and no server of your own is needed for it.
Then — and this is the step — you copy the RuName that eBay generated for that entry. It is a short opaque string sitting next to the URL you just typed. The field that wants it is surrounded by URL fields, so the instinct is to paste the URL again. That does not authorise, and the error you get back does not say why.
The sandbox is not a shortcut
eBay runs a sandbox that needs only a free developer account, with no seller account in good standing, and it is genuinely useful for learning the shape of the API. It is not useful for the thing you actually want, which is your own listings and your own orders. Sandbox data is synthetic.
New connections in Orkas use production only. That means the eBay Developers Program application — an app with seller account, inventory, listing and fulfilment permissions, and its Production Keyset — is the long pole in this setup, not the client you pick afterwards. Start it early. The official authorisation guide is worth reading while the application is pending.
Reading is not writing
Once the keyset exists, the permission list decides what the connection is actually for. Asking what sold last week is a read. Revising a listing, adjusting inventory or marking an order shipped is a write, and it needs the corresponding scopes on the app.
Several hosted eBay-to-Claude services are read-only by design, and that is a reasonable product — it is just not the same product. Check the write side before you invest the application effort, because the application in front of it is identical either way.
The Orkas connector runs against the production Sell APIs from your own machine. Credentials are encrypted on the device rather than living in a config file or on someone else's servers, and anything that writes to a live account goes through a permission prompt in the client instead of relying on the model to be cautious.
When something else is the better answer
You only want reports: a hosted connector is less setup and there is nothing to install. You want it running on a schedule with nobody watching: this is a desktop application, so closing the window stops it; a scheduled job on a server is the right shape. You are still learning the API: use the sandbox and a free developer account, and do not connect anything to a live account yet.
The same catalogue covers Etsy, Walmart Marketplace, Amazon Seller Central, Shopify, WooCommerce and the Chinese platforms, so the credential-juggling does not restart once per storefront. The neighbouring write-ups on Etsy and Shopify cover the same ground for those two.