Turn on/off relay

I'm trying to turn a relay on and off, from a program I made in C#. Me When I click on the button I see the "RX" led of the ArduinoBoard turning on, that is, something comes to the Arduino, but the relay never comes on... I don't know what I'm doing wrong

C# Code

Class forms:

private void ACClick_Click(object sender, EventArgs e)
    {
        if (AC)
        {
        
            Arduino.SendInfo(Convert.ToString(AC));
            this.ArCondicionado.BorderStyle = BorderStyle.FixedSingle;
            AC = false;
        }
        else
        {
            Arduino.SendInfo(Convert.ToString(AC));

            this.ArCondicionado.BorderStyle = BorderStyle.None;
            AC = true;
        }
    }
}

Class to control my arduino info:

 class Arduino
{
    static SerialPort Port;

    public static int ConnectArduino()
    {
        int ArduinoPort = 0;

        try
        {
            if (Port == null)
            {
                Port = new SerialPort();
                Port.PortName = "COM3";//Set your board COM
                Port.BaudRate = 9600;
                Port.Open();
                ArduinoPort = 1;
            }
        }
        catch (Exception e)
        {

            Console.WriteLine("{0} Exception caught.", e);
            MessageBox.Show("O Arduino not connected", "Erro", MessageBoxButtons.OK, MessageBoxIcon.Error);

        }
        return ArduinoPort;

    }
   public static void SendInfo(string message)
    {
        try
        {
            if (Port != null && Port.IsOpen)
            {
                Port.Write(message);
                Console.WriteLine(message);
            }

        }
        catch (Exception e)
        {
            Console.WriteLine("Exception information: {0}", e);
            throw new Exception(e.ToString());
        }
    }
}

Arduino code:

 #include "ArduinoJson.h"
  StaticJsonDocument<200> doc;
  #define relayO 7

  void setup() {
    pinMode(relayO, OUTPUT);
    digitalWrite(relayO, HIGH);
    Serial.begin(9600);
  }

  void loop() {
    if (! Serial.available()) return;
    String json = Serial.readString();
    deserializeJson(doc, json);
    JsonVariant RelayInfo = doc["AC"];
    if(!RelayInfo.isNull()) {
      if(RelayInfo=="True") {
        digitalWrite(relayO,HIGH);
      }
      else{
        digitalWrite(relayO,LOW);
      }
    }
    delay(1000);
  }

Have you tried printing what the Arduino receives ?
Is it what you expect ?

verify that the code can toggle the realy

void setup() {
    Serial.begin(9600);
    pinMode(relayO, OUTPUT);

    while (1)  {
        digitalWrite(relayO, HIGH);
        delay (1000);
        digitalWrite(relayO, HIGH);
        delay (1000);
    }
}

and as bob suggested, verify what is received

Receives a json with an object "AC" that has an assumed value (true or false but the type is a string).
I can't open the serial port in arduino IDE and connect to arduino (with my c# code), because it don't let's me use the same COM port on 2 different things. I don't know if I'm making myself understood

The relay is working I made a code similar to that was working fine. The problem is the Arduino interpret the information receives