User name or password is incorrect when performing domain join to Azure VM

1. Installed AAD Domain Services with domain name "mydomain.com"
2. Added verified custom domain "mydomain.com"
3. Made "mydomain.com" primary
4. Created AAD user "admin@mydomain.com"
5. Converted temp password to permanent password
6. Logged into Azure with permanent password
7. Added "admin@mydomain.com" to domain administrators group
8. Ensured VM can see domain services for "mydomain.com"
9. When performing domain join, receive "The user name or password is incorrect"

I've tried the following credential combinations when doing the domain join (username : password)

1. admin : pwd
2. admin@mydomain.com : pwd
3. mydomain.com\admin : pwd
4. mydomain.com\admin@mydomain.com : pwd

None of these work and ultimately give me a lock out indication.  I create additional users to continue trying these steps but nothing is working.

Stephen