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Please note that there is currently a bug in the SP Dashboard that prevents you from using a custom URL scheme. You can contact support in case you need it.

Although supported, the advice is to register an application specific URL, please refer to "Mobile apps" below on how to do that.

Ip addresses cannot be used in redirect URLs, unless it's 127.0.0.1 or [::1]

Localhost

In We discourage the use of localhost redirect URLs. Only in cases when you are developing, or when you have a native desktop app, we support localhost redirect URLs. Since this traffic never leaves the host machine, the http:// scheme is allowed here.
You may use http://127.0.0.1 or the ipv6 equivalent, http://[::1]. Port numbers are allowed too. On production, you should only use this for native apps.

Native apps

On mobile apps, we advise you to register application specific URLs for your redirect URL (in stead of using localhost). For Android, you can check https://developer.android.com/studio/write/app-link-indexing. For Apple, check their documentation on https://developer.apple.com/documentation/xcode/allowing_apps_and_websites_to_link_to_your_content

For more information on the current best practices on native apps, please refer to rfc8252