I followed the this tutorial to set up Azure B2C on my MSDN subscription. But it failed with the error:

To resolve this, I needed to add the namespace Microsoft.AzureActiveDirectory to my subscription. This article documents the steps I took.
- Use the Azure Cloud Powershell terminal or Powershell on your PC
- Ensure you have the Azure CLI tools installed on your PC if you will use the local Powershell terminal
- Log into you azure account:
az login
- Specify the subscription you want to work on. Get a list of your subscriptions:
az account list
- Once you have identified your required subscription, you will need to set it e.g. if your subscription name is “Company-Production”:
az account set --subscription "Company-Production"
- Now, register the required namespace provider:
az provider register --namespace Microsoft.AzureActiveDirectory
Now you will be able to continue using this tutorial to create an Azure B2C tenant.