I can confirm to everybody that the syntax is correct. Assuming "prova" to be the name of my vman, then the output of the autocomplete command, "?", after the keyword "untagged" is , i.e. no port-cvid is expected:
* X150-001.1 # configure vman prova add port 1 untagged ?
Execute the command
So, we can finally conclude that the "port-cvid" parameter of the command:
configure vman vman-name add ports [ all | port_list ] {untagged {port-cvid port_cvid} | tagged}, as described in the user guide is not supported by 15.3.2 on x150.
Unfortunately, we don't have x460 or older OS versions.
Thanks to all.