mysqli transaction doesnt work

Question

so, i need to insert data into 2 tables the second needs the autoincremented user_id from table 1
i have turned autocommit to false i believe yet the code only stores the username and password.
where ami going wrong?
<?php
require_once ("encrypt.php");
$conn = mysqli_connect($servername, $dbuser, $dbpassword, $dbname);
$problem = '';
$firstName = $_SESSION['firstName'] ;
$lastName = $_SESSION['lastName'];
$email = $_SESSION['email'];
$username= $_SESSION['username'];
$password= $_SESSION['password'];

$pass = encrypt($password);

if(isset($_POST["mysubmit"]) && ($_POST["mysubmit"]=="Submit Form")){
$eventDate = mysqli_real_escape_string ($conn, $_POST["eventDate"]);
$difficultyCatagory = mysqli_real_escape_string ($conn, $_POST ["difficultyCatagory"]);
$clubSelect = mysqli_real_escape_string ($conn,$_POST["clubSelect"]);
echo $eventDate, $difficultyCatagory, $clubSelect, $firstName, $lastName, $email, $username,$password;

if ($problem == ''){

mysqli_autocommit($conn,FALSE);

mysqli_query ($conn,"INSERT INTO userBMX (username,password)
VALUES ('$username', '$pass')");

mysqli_query ($conn,"INSERT INTO userDetailsBMX (userID , firstName, lastName, email, dateofBirth, Status, club)
VALUES (last_insert_id(), $firstName, $lastName, $email, $eventDate, $difficultyCatagory, $clubSelect)");

mysqli_commit($conn);
mysqli_close($conn);

echo 'stored';
}
else{
echo "ERROR: was not able to execute $conn. " . mysqli_error($conn);
}
}
?>

Answer 1

all the variables echo perfectly