You should be using the same modbus address that you use when connected to the computer.
Looking at the datasheet again, I told you the wrong connections. I’m sorry. Only Y/Z are available in half-duplex mode, not A/B. So you need to move A->Y and B->Z. Turn off the Y/Z termination dip switch (I think). I also told you the wrong pins for DE/REnot. They should be A5/A6 *not* A4/A5.
If fixing the wrong connections I told you to use doesn’t fix things, try disconnecting A5 and A6 and manually setting them at the start of your program. Set
DEREPin = -1; Then in your setup function, add this:
Since it is a fully duplex chip, both the receiver and driver can be enabled at the same time, unlike half-duplex chips like the MAX485.