A 40-character identifier supplied by eBay to an application. Used to confirm the identities of the user and the application in a URL redirect during the process in which the user agrees to let the application wield a user token that grants the application the right to access eBay data on behalf of the user. Subsequently also used as input for the FetchToken API call. The SessionID is valid for five minutes after it is retrieved.
See the Field Index to learn which calls use SessionID.