Using a Crowtail Volt sensor

I have a crowtial Voltage sensor and I am trying to read votlage with my Sodaq ONE:

Here is a doc that makes 0 sense to me : https://www.elecrow.com/wiki/index.php?title=Crowtail-_Voltage_Sensor

I tried this too but its either 0 or very random numbers, nor corerect;

int VOLTMETER = A2;
int VoltageValue = 0;
void setup() {
SerialUSB.begin(9600);
pinMode(ACC_INT_PIN, INPUT);
}

void loop() {
int VoltageValue = analogRead(VOLTMETER);
float voltage = (VoltageValue / 1024) * 3.6;
SerialUSB.println(voltage);
SerialUSB.print(" ");
delay(1000);
}