Same issue here! Email works fine, but github does not.
Auth0 App callback: https://spendless.io/callback/
Github OAuth App callback: https://spendless.io/callback/
Application Type: Single Page Application
(followed this tutorial How to Secure GatsbyJS Sites with Auth0 for Authentication)
gatsby 2.19.12
auth0-js 9.12.2
Same error when trying to login to both the app and the “Try It” button in manage.auth0.com/dashboard/us/*******/connections/social
https://spendless.io/callback/?error=redirect_uri_mismatch&error_description=The+redirect_uri+MUST+match+the+registered+callback+URL+for+this+application.&error_uri=https%3A%2F%2Fdeveloper.github.com%2Fapps%2Fmanaging-oauth-apps%2Ftroubleshooting-authorization-request-errors%2F%23redirect-uri-mismatch&state=Z*************