One-time developer setup — like ShipStation does behind the scenes. After this is filled in, connecting a store is a single click: the user just signs into the marketplace and clicks Agree. These keys are encrypted in the local vault and never shown to store users.
One-time setup: 1) copy the Production App ID / Cert ID from Application Keys. 2) Under User Tokens, create an OAuth Redirect URI (RuName) whose Auth accepted URL is https://YOUR-DOMAIN/oauth/callback/ebay. 3) Paste all three values here. Afterwards, connecting an eBay store is a single click.
One-time setup: register your SP-API application and IAM role, then paste the IDs/keys here. After that, connecting an Amazon store is a single click.