Is there anyone here knows how to install this on an inverter? I haven't been able to locate an instruction manual.
You need to follow the labeling and instructions which were part of the equipment's UL, TUV, ETF etc. listing... nope, could not keep a straight face.
Seriously, the labeling and instructions that is actually on your equipment. If that's the lower picture, then the current transformer goes on 5 and 6, line to 1 and 2, and neutral to 3 and 4.
Do not daisy chain, that is don't bring "line in" into 1, and "line out" into 2, unless your diagram tells you to (such as in your first picture). In the lower pictured unit, you need to put pigtail wires on line 1 and 2, and use an appropriate 4-wire splicing device to join those pigtails to line in and line out (4 wires in total). Likewise lines 3 and 4. Note the instruction may be different for line vs neutral. That's for a reason.