Called before an import begins. In the case of an OAuth import, this callback executes when the user is directed to the OAuth flow. For other import methods, it fires when the user submits their data (either a file or their credentials).
This callback includes the source and importId of the address book being imported. This is handy if you want to send the user away and process the address book in the background.
This event fires even if the import fails. In most cases a failed import can be detected by querying the /events endpoint with the importId.
The importId is not always defined. For example, when the contact picker fails to authenticate with our service. Be sure to handle an undefined importId gracefully.