I too had this issue. Took a while to figure out that the RJ-45 to DB9 is not standard connection. So you have to change the pins somewhere. bigDvette's pins are not correct (depending on how you view it). Pin1 & Pin8 are swapped. The correct pin outs are:
RJ45/PLM Pin 1 --> RS232 Rx (Computer Side Pin 2)
RJ45/PLM Pin 8 --> RS232 Tx (Computer Side Pin 3)
RJ45/PLM Pin 7 --> RS232 Gnd (Computer Side Pin 5)
https://www.manualslib.com/manual/1447637/Insteon-Powerlinc-2413s.html#manual