Why does SQL show the following error while Updating table

I am trying to update a SQL table using data from an HTML form but am getting the following error:

This is how I handle the POST request for my Form:

$con = mysqli_connect("localhost", "root", "", "lectureHub");
if (isset($_POST['rating'])) {
    $likert = $_POST['likert'];
    $feedback = $_POST['feedback'];
    $chapter_id_fk = $_POST['chapter_id_fk'];
    $page_id_fk = $_POST['page_id_fk'];
    //echo "Entered data successfully. Click on LectureHub tab to see the Lecture";
    $sql = "UPDATE pages SET likert = $likert, feedback = $feedback WHERE chapter_id_fk = $chapter_id_fk and page_id = $page_id_fk";
    $retval = mysqli_query($con, $sql);
    if (!$retval) {
        die('Could not enter data: ' . mysqli_error());
    }
    $sql_page_id ="select page_id_fk from pages where chapter_id_fk = $chapter_id_fk and page_id = $page_id_fk ";
    $result = mysqli_query($con,$sql_page_id);
    if ($result->num_rows>0){
        while($row = $result->fetch_assoc()){
            $page_id_fk = $row['page_id_fk'];
            echo "<script> window.location = 'index.php?action=lec_hub/pages&page_id=$page_id_fk&chapter_id=$chapter_id_fk'; </script>";
        }

    }
    //echo "<script> window.location = 'index.php?action=lec_hub/pages&page_id=$sql_page_id&chapter_id=$chapter_id_fk'; </script>";
}

Could someone explain me why am I getting the error and how can I resolve it?