Schneider Electric M221 + Remote Modbus Slave (Serial)

Hello new user here seeking some guidance. I have been given the task of polling data from a modbus slave (Thermo 43i Analyzer) using RS-232. Unfortunately I can not get the Read_Var function to work or the Modbus Serial IOScanner to work.... I am trying to read holding registers using modbus command 0x03. Any help would be much appreciated as the program (Ecostruxure Expert - Basic) does not have much for tutorials when it comes to establishing this communication.

Thanks

Here is some information that helped me.
All you need to know about Modbus RTU.
https://www.youtube.com/watch?v=OvRD2UvrHjE
About Modbus
https://www.simplymodbus.ca/FAQ.htm
Once you know the basics then you can look at setting up the M221 as the master (client)
https://damrexelprod.blob.core.windows.net/medias/241f740c-630a-42ce-8195-4ba057a1871e
Set up your slave (server) on the Thermo 43i Analyzer. Ensure that the serial communication matches and the unit number has been set.
I hope this helps you out.
Regards,

-> Check serial config: baudrates/parity/data bits/...
-> Check CommError and OperError which READ_VAR provides
-> Check device id (modbus address) if it matches with the device
-> Check the block size limitation, some devices does not allow you to read an entire block in a single request, for example reading the following block might not be possible, some also does not allow reading only 40001 since it is a Float32 or a Dword it forces reading the entire datatype.

40001&40002 SO2 CONC
40003&40004 NOT USED
40005&40006 NOT USED
40007&40008 LO SO2 CONC (Dual/Auto Range mode)
(This section is taken from Thermo 43i Analyzer specs)