Modbus TCP request timeout

I'm using https://github.com/simonvetter/modbus. I'm able to open a connection with the device, but requests to read registers always timeout.

My first time using modbus. Can anyone tell me what the issue might be?

Code:

package main

import (
    "fmt"
    "os"
    "time"
    "github.com/simonvetter/modbus"
)

func main() {
    client, err := modbus.NewClient(&modbus.ClientConfiguration{
        URL:      "rtuovertcp://192.168.50.60:502",
        Speed:    19200,
        Parity:   modbus.PARITY_NONE,
        DataBits: 8,
        StopBits: 1,
        Timeout:  1 * time.Second,
    })
    if err != nil {
        fmt.Println("Error creating Modbus client:", err)
        return
    }

    // tried with and without setting this
    client.SetUnitId(100)

    err = client.Open()
    for err != nil {
        fmt.Println("faild to open", err)
        os.Exit(1)
    }
    defer client.Close()

    var addr uint16
    var reg16 uint16

    // tried many different addresses and also tried modbus.INPUT_REGISTER
    addr = 100
    reg16, err = client.ReadRegister(addr, modbus.HOLDING_REGISTER)
    if err != nil {
        fmt.Println("ReadRegister:", err) // err == "request timed out"
        os.Exit(1)
    }

    fmt.Printf("address: %v", addr)
    fmt.Printf("   value: %v", reg16)          // as unsigned integer
    fmt.Printf("   value: %v", int16(reg16))   // as signed integer
    fmt.Printf("   value: %v", float32(reg16)) // as float
}

The device has an interface that shows I've connected and its received data, but sent nothing back. (RX > 0, TX == 0)

Wireshark capture: Sent data (8 bytes): 01 03 00 64 00 01 c5 d5

The device configuration:

EDIT: tried Modbus TCP with the same result:

    client, err := modbus.NewClient(&modbus.ClientConfiguration{
        URL:     "tcp://192.168.50.60:502",
        Timeout: 1 * time.Second,
    })