Conversely, Production keys cannot be used to make API calls in the Sandbox.)

(Keys for the Sandbox cannot be used to make API calls in the Production environment. The keyset for the Sandbox is different from the keyset for the Production environment. Once you join the eBay Developers Program, you can Create the eBay API keysets for your application. For the simple registration procedure, see Join the eBay Developers Program. The first step is to register with eBay as a developer. In order to obtain your application keys and start developing your application, you must join the eBay Developers Program. For additional information, see Understand application keysets. You use these keys to generate an authentication token for a user.

Application keys consist of a set of data that identifies the application and its developer. These IDs are referred to as application keys (because they unlock the door into the particular application environment). For an application to be able to operate in the Sandbox or the Production environment, it needs to have the appropriate IDs for that environment.

How to create a application id in ebay