What library did you end up using? I'm fighting a similar issue with trying to read modbus regs on a Wattnode with my Tracker SoM and getting an E2.
Neither the modbus-master or the modbus-master-particle libs did it for me.
I'm getting the correct serial out via my tx, but when I try interfacing with
my 485 breakout board options, nothing intelligible comes out of the 485 end. Option 1) SparkFun Transceiver Breakout - RS-485 - BOB-10124 - SparkFun Electronics
or 2)Amazon.com
I've even hooked up a usb 485 receiver to the 485 end. Ultimately, the stuff coming off the 485 bus is gibberish, which is what I've been really frustrated with. I'm thinking about picking up a chip that doesn't use the rst piece.