Quickbooks returns an extremely important piece of information “the realmid” in the query parameter below which is the unique customer ID. This is the only way to retrieve the realmId from quickbooks when a new company logs in.
realmId parameter on the redirect URL passed during the OAuth 2.0 authorization request.
https://[your auth0 instance].us.auth0.com/login/callback?code=AB11677294234&state=9rT_so&realmId=4620816365
How would I retrieve this realmId?