I have an Azure subscription where the subscription administrator account is a Microsoft Account. I then added another Microsoft Account as a co-administrator. I\'m told tha
For those that run across this question in the future, the previous answer still appears to be correct. Basically, you have to create a new account that is native to the directory. This account can be used to login when running connect-msolservice in PowerShell, and then you can run set-msoluser to convert the user from "Guest" to "Member".
The following blog post has detailed step-by-step directions to do this. Note that you need to follow the Appendix first if your Global Admin account is not a work or school account. Also, I've added a few important details in the Comments section of the blog post.
https://blogs.msdn.microsoft.com/dstfs/2015/12/23/issues-with-azure-active-directory-guest-users-in-aad-backed-visual-studio-team-services-accounts/
For reference, a similar problem and resolution using set-msoluser can be found in this forum post: https://social.msdn.microsoft.com/Forums/azure/en-US/469baa2d-7ff1-4e17-a8f0-f257cbdbf50b/cannot-see-the-active-directory-item-in-the-azure-portal?forum=WindowsAzureAD