Tinboye we just got word back from our secondary developer that you are not required to fill in this field for Discord Connect as there are no interactions between the platform and Discord other than the OAuth 2 connection of services.
So again, if you are on the General Information tab of your DIscord application settings "Interaction Endpoint URL" should be blank, and your callback URL that is generated from Discord Connect should be placed under "Redirects. of the OAuth tab.
To add support for another type of storage you need to create file inc/class/BxDolStorage1fichier.php and implement all necessary methods to add/get/delete/etc files. To get list of methods you need to implement please refer to inc/class/BxDolStorageS3.php.