Make sure the domain details provided are valid and the domain controller is reachable from the subnet used for RemoteApp. ...

Make sure the domain details provided are valid and the domain controller is reachable from the subnet used for RemoteApp. Also make sure the service account credentials supplied have permission to add computers to the provided domain and the AD name provided can be resolved from the DNS provided in VNET. For more details on how to validate the VNET and connectivity to DC, please visit our technical articles.