Azure Access Control needed but it's greyed out

I am setting up a SharePoint 2013 onprem installation using server to server based authentication with CRM 2015 online. As per Microsoft instructions I need to setup a ACS control namespace in Azure as it is a requirement for the authentication/tokens between SharePoint and CRM. The option in Azure is greyed out and under it says "not available." How do I enable this option? What features are needed to be added to Azure in order to make the ACS namespace? The Microsoft article does not say and I can't seem to find the information online. I have signed up for the Azure AD free account. If I add the pay as you go plan, will the ACS control function become enabled?

Thanks,

Jon Peterson