I'm not from electronics background so I don't know what should be the connections. My Hall sensor has 4 pins(AO, GND, +, DO)

So, I have connected hall sensor pins to Arduino nano pins in this order(connection)

AO(Sensor) <-> A4(Arduino)   [Changed from A0 to A4]
DO(Sensor) <-> D4(Arduino)   [Changed from D0 to D4]
+(Sensor) <-> 5V(Arduino)
GND(Sensor) <-> GND (Arduino)

What should be pseudo code? So that if the magnet passes close to the sensor. Arduino should get the output & I'll blink the led on Arduino

This below is my code that I have written so far

int sensorPin = 4; // this is for sensor in analog pin 4
int buttonPin = 4; // we are looking for digital 4
int val;

bool flag = false;

void setup() {
  // put your setup code here, to run once:
  pinMode(buttonPin, INPUT); // defines digital pin 4 as input for LED
  Serial.begin(9600);  
}

void loop() {
   int reading = analogRead(sensorPin);

   float voltage = reading * 5.0;
   voltage /= 1024.0;

  if(voltage > 3.0) {
   Serial.print(voltage); Serial.println("volts");
  }
   val = digitalRead(buttonPin);  // read data from digital Pin

   if(val == HIGH) // when the sensor detects a magnetic field
   {
      flag = !flag;
      if(flag){
         digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
      } else {                 // wait for a second
          digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
      }
      //delay(1000);                       // wait for a second
   }
   delay(100); 
}

Expected output: It should turn On/Off the LED when voltage goes HIGH

Known issues: It works sometime. It doesn't work sometime. Also it works only when magnet is kept clone. Doesn't detect when I'm waving magnet close to the sensor