I did follow the steps in the doc you mentioned.
See below the commands I tried.
I ran these commands when the Matser one is powered on and the second switch is powered off as it is mentioned in the doc.
root@:RE:0% set preprovisioned
root@:RE:0% set virtual-chassis member 1 serial-number BM0211335826 role line-card
set: Syntax Error.
root@:RE:0% set member 1 serial-number BM0211335826 role line-card
set: Variable name must begin with a letter.