Problem with slider value sending it to php

I have this slider:

<form id="sliderForm1" action="registerValidation.php" method="POST">
  <label for="sliderValue1">Kiek su tuo sutinkate?:</label>
  <output id="sliderOutput1" name="sliderOutput1">0</output>
  <input type="range" min="0" max="100" value="0" id="sliderValue1" name="sliderValue1">
</form>

I have some javascript file, for checking lines, but its not essential here, there are no modification of values.

I try putting it to database:

$password_hash = password_hash($_POST["password"], PASSWORD_DEFAULT);


$mysqli = require __DIR__ . "/databaseConnect.php";


$sql = "INSERT INTO user (username, email, password_hash, slider1Value) VALUES (?, ?, ?, ?)"; //////////////!!!!!!!!!!!!!!!!!!!/////////////////////

try 
{
    $stmt = $mysqli->prepare($sql);
    $stmt->bind_param("sssi", $_POST["username"], $_POST["email"], $password_hash, $_POST["sliderValue1"]); //////////////////////////////////////////////
    $stmt->execute();
    header("Location: login.php");
    exit;
} 
catch (mysqli_sql_exception $exception) 
{
    if ($mysqli->errno === 1062) //dublicate key element error number
    {
        die("El. pašto adresas arba vartotojo vardas jau užimtas");
    } 
    else 
    {
        die("Klaida: " . $exception->getMessage());
    }
}

DB view:
Db view

But I keep getting an error: Column ‘slider1Value’ cannot be null.
I tried to change value manually, tried to give output values to $stmt.