Reading PLC register using ModBusTCPCom in .Net results in address not found

I have to update an old WinForms application. The application uses the AdvancedHMI .NET software. I am connecting to the PLC (AutomationDirect DirectLogic 06 Series) with no issues, and various other registers are being read accurately. I am expecting to get a 4 digit value from the register.
I am reading it like so:

Dim rawValue As String = BeltSpeedModbusTcpCom.Read("V3103")

When I read the register I get address not found.

The ladderlogic diagram I am was given is:

I have tried adjusting the address, using 03103, F3103, and other combinations. We can view the address values in real time in the PLC using software the customer has.

According to Page 4-13 of the DL-06 manual, the “V” register number is Octal. Try reading “1603”, which is octal 3103 converted to decimal.