AzureAD Failure 2313

Hi All,
Spun up a new Azure Server 2019, and trying to authenticate using AzureAD user accounts for server login for the first time using that new preview functionality.
I've verified that the users have the "Virtual Machine Administrator Login" role, and that the PC trying to RDP From is AzureAD Registered.
However, I can't get any users to finish authentication properly. In the server logs, the RDP log identifies that an attempt to login happened, but did not complete. In the security log, I get the failure shown below. Through some Googling it is suggested that the error code & sub-error code mean that the user account does not exist. I tried adding the user accounts right on the server as "Work or school users" just in case, but it still throws the same error.
Any thoughts?
- System
-
EventData
SubjectUserSid
S-1-0-0
SubjectUserName
-
SubjectDomainName
-
SubjectLogonId
0x0
TargetUserSid
S-1-0-0
TargetUserName
username@keyman .ca
TargetDomainName
AzureAD
Status
0xc000006d
FailureReason
%%2313
SubStatus
0xc0000064
LogonType
3
LogonProcessName
NtLmSsp
AuthenticationPackageName
NTLM
WorkstationName
My_Workstation
TransmittedServices
-
LmPackageName
-
KeyLength
0
ProcessId
0x0
ProcessName
-
IpAddress
216.223.79.xx
IpPort
0