struct.error: bad char in struct format

[TristanLowell]

I have been working with chatgpt to try and figure this out but to no avail. What is really confusing is the req and res seems correct and the last DEBUG:pymodbus.loggging line shows [60] which is the correct value in that register. how come the bad struct?

OS: linux (paired down on an IOT cell router)
pymodbus: 3.7.4, serial, sync

logs/output:
~ # ./mqtt_mbus_serial.sh
DEBUG:paho.mqtt.client:Sending CONNECT (u0, p0, wr0, wq0, wf0, c1, k60) client_id=b'a44058a7-e58f-438d-9578-71576b88cffb' properties=None
get and verify data
DEBUG:pymodbus.logging:Current transaction state - IDLE
DEBUG:pymodbus.logging:Running transaction 0
DEBUG:pymodbus.logging:SEND: 0x1 0x3 0x0 0x31 0x0 0x1 0xd5 0xc5
DEBUG:pymodbus.logging:New Transaction state "SENDING"
DEBUG:pymodbus.logging:Changing transaction state from "SENDING" to "WAITING FOR REPLY"
DEBUG:pymodbus.logging:Changing transaction state from "WAITING FOR REPLY" to "PROCESSING REPLY"
DEBUG:pymodbus.logging:RECV: 0x1 0x3 0x2 0x0 0x3c 0xb8 0x55
DEBUG:pymodbus.logging:Processing: 0x1 0x3 0x2 0x0 0x3c 0xb8 0x55
DEBUG:pymodbus.logging:decode PDU for 3
DEBUG:pymodbus.logging:Frame advanced, resetting header!!
DEBUG:pymodbus.logging:Adding transaction 0
DEBUG:pymodbus.logging:Getting transaction 0
DEBUG:pymodbus.logging:Changing transaction state from "PROCESSING REPLY" to "TRANSACTION_COMPLETE"
DEBUG:pymodbus.logging:[60]
Traceback (most recent call last):
File "/root/mqttMbus/main.py", line 80, in
main()
File "/root/mqttMbus/main.py", line 71, in main
mbusDataPacket = mbus.mbusPollilng(mbus, slaves)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/root/mqttMbus/mbus/mbus.py", line 254, in mbusPollilng
measureDict["data"] = {"n-value" : mbusObj.mbusConnect(SlaveDefFile[i]["Type"], SlaveDefFile[i]["Address"], SlaveDefFile[i]["NumRegisters"], SlaveDefFile[i]["SlaveId"], SlaveDefFile[i]["DataType"])}
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/root/mqttMbus/mbus/mbus.py", line 190, in mbusConnect
outDat = decodedValue()
^^^^^^^^^^^^^^
File "/opt/python3/lib/python3.11/site-packages/pymodbus/payload.py", line 397, in decode_16bit_int
return unpack(fstring, handle)[0]
^^^^^^^^^^^^^^^^^^^^^^^
struct.error: bad char in struct format

[TristanLowell]

The issue was wordorder and byteorder were not set properly. once i had those values aligned with the sensor i was using the request and response from the modbus engine worked as expected.