Obvious question, but I need to ask anyway, have you power cycled the flow meter? Many devices need to be power cycled for any setting changes to take effect.
Try a changing the baud rate, parity, and slave address on both your Modbus software and the flow meter, power cycle to the flow meter, then try communicating again. I've seen bugs in some equipment where certain parity or baud rate settings don't actually work.
What is the vendor and model of the flow meter? Does the vendor supply PC software that can communicate to the flow meter via a USB to RS-485 adapter?
Try a changing the baud rate, parity, and slave address on both your Modbus software and the flow meter, power cycle to the flow meter, then try communicating again. I've seen bugs in some equipment where certain parity or baud rate settings don't actually work.
What is the vendor and model of the flow meter? Does the vendor supply PC software that can communicate to the flow meter via a USB to RS-485 adapter?