You must run the vdmadmin command as a user who is in the Administrators role for a specified action to succeed.
You can use Horizon Administrator to assign the Administrators role to a user. See Configuring Role-Based Delegated Administration.
If you are logged in as a user with insufficient privileges, you can use the -b option to run the command as a user who has been assigned the Administrators role, if you know that user's password. You can specify the -b option to run the vdmadmin command as the specified user in the specified domain. The following usage forms of the -b option are equivalent.
-b username domain [password | *]
-b username@domain [password | *]
-b domain\username [password | *]
If you specify an asterisk (*) instead a password, you are prompted to enter the password, and the vdmadmin command does not leave sensitive passwords in the command history on the command line.
You can use the -b option with all command options except the -R and -T options.