OutOfRange in some array, write doesn't work

Main.cs

@@ -474,6 +474,7 @@ namespace Gidrolock_Modbus_Scanner
                     switch ((FunctionCode)functionCode)
                     {
                         case (FunctionCode.WriteCoil):
+                            Console.WriteLine("Trying to force single coil");
                             if (valueLower == "true" || valueLower == "1")
                                 await Modbus.WriteSingleAsync(port, (FunctionCode)functionCode, (byte)UpDown_ModbusID.Value, (ushort)address, 0xFF_00);
                             else if (valueLower == "false" || valueLower == "0")

Modbus.cs

@@ -55,6 +55,7 @@ namespace Gidrolock_Modbus_Scanner
                 GetCRC(_message, ref CRC);
                 _message[6] = CRC[0];
                 _message[7] = CRC[1];
+                Console.WriteLine("Message: " + ByteArrayToString(_message));
                 return _message;
             }
             else return new byte[1] { 0xFF };
@@ -129,6 +130,7 @@ namespace Gidrolock_Modbus_Scanner
             try
             {
                 port.Write(message, 0, message.Length);
+                Console.WriteLine("Write message sent successfully");
                 return true;
             }
             catch (Exception err)