Are they referring to the large positive battery connection post? Underlined below at the last sentence
Cable for Smart BMS CL 12-100 to MultiPlus (PN: ASS070200100)
This cable will allow the MultiPlus 500VA – 1600VA, MultiPlus Compact 800VA – 2kVA and MultiPlus-II models to be used with BMS products that have no VE.Bus interface, such as the Smart BMS CL 12-100 and the smallBMS. These MultiPlus models can be controlled from the Load/Charge Disconnect outputs and Load/Charger outputs respectively.
The cable must be wired to the remote on/off connector of the MultiPlus models:
• When used with the MultiPlus 500VA-1200VA models connect the black wire to the ON terminal and the red wire to the (+) terminal.