Azure: subscription not registered for a resource provider namespace

TL;DR: The subscription is not registered to use namespace 'Microsoft.X'. New subscriptions and new services need explicit registration; the error names the exact namespace to register. Fix: Wait until Registered (can take minutes). Verify: az provider show says Registered, then the original create command succeeds.

The fix

1. New subscriptions register only a common subset. The first AKS, the first Key Vault with certain features, the first Data Factory in a sub all hit this.
2. Terraform/Bicep. The azurerm provider can auto-register (resource_provider_registrations = "core"), but explicit registration in your bootstrap script is more predictable than relying on provider behavior.
3. Permission. Registering needs Contributor on the subscription (or the specific Microsoft.Resources/subscriptions/resourceGroups write). A service principal with only resource-group scope cannot self-register; register from a broader identity first.
4. Do not confuse with feature flags. Some services need both provider registration AND a preview feature flag (az feature register). If registration succeeds but creation still fails, check for a feature flag. Verify: az provider show says Registered, then the original create command succeeds.

When to use this

• This covers exactly what the title says: Azure.
• You are setting this up for the first time, or auditing an existing setup.
• You want the key gotchas in one place before you start.

When not to use this

• You are doing a different workflow with Azure; these steps are specific to the title above.
• You need the full reference docs; this is the short path, not the manual.

Compatibility

• Not pinned to a specific version; follows current Azure behavior.

Proactive error-catalog skill. Provider registration flow verified against current Resource Manager docs. Evidence: https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-providers-and-types