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Both are mutually exclusive. This means that a project cannot have platform users and Realm users simultaneously.
2.1 Linking a Realm and importing associated users
If you want to manage users in a project from a Realm, leave the checkbox checked, and select a Realm from the list and click on 'Link Realm':
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You can unlink the Realm at any time by clicking 'Unlink Realm', but if the resources are already shared, they will be removed!
2.2 Adding platform users
If you would rather choose to import users to the project from the platform, then uncheck the checkbox ('Link with the realm'). You will notice a new combo appearing.
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