set virtual-chassis command is not working for me on EX4200

Hi,

I'm following this doc (https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/virtual-chassis-ex4200-cli.html#jd0e48) for configuring an EX4200 Virtual Chassis.

But in the step 8:

After typing "set member 0 serial-number abc123 role routing-engine" command, I am getting this error:

set: Variable name must begin with a letter.

If I type this "set virtual-chassis member 0 serial-number abc123 role routing-engine"  command, I am getting an error as well:

set: Syntax Error.

Any ideas why the "set" command is working working for me?

Thanks!