I have a similar issue. I just purchased the Kodak VMIII inverter and a Pylontech us3000c battery.
I am using the cable supplied with the inverter (and the side labeled PYLON is connected to the battery). I checked the pins to what is suggested in this forum and it seems to correspond.
I have selected PYL as the battery type.
I am still receiving the 61 error.
Could it be possible that the us3000c has a different pinout?