Hi Norbert Bonnici,
You can register the Microsoft Azure Stack HCI resource provider with a subscription through using the Azure Portal, Azure CLI, or PowerShell.
- Sign in to the Azure portal.
- On the Azure portal menu, search for Subscriptions. Select it from the available options.
- Select the subscription you want to view.
- On the left menu and under Settings, select Resource providers.
- Find the resource provider (Azure Stack HCI) you want to register.
- Select the resource provider to see the details of the resource provider.
- Select the resource provider and select Register. To maintain least privileges in your subscription, only register the resource providers that you're ready to use.
For more detailed information, please check: Azure resource providers and types
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