如何在我的函数上修复“在字符串上调用成员函数execute（）”

I'm modifying a Wordpress API witch is currently getting learnpress course and lessons infos from the database using leanrpress functions only. I need to modify the API to get the scores from the newly implemented plugin h5p, therefor i need to make a new function to access the Database and get the scores from the right table, then put then into an array with the according lesson. The array here is only an exemple i'm using to see if i can get the datas, ut i'm stuck with the error

"Call to a member function execute() on string"

when i try and run it on postman. Could someone lighten me on this issue please ?

function ilp_api_get_progress_by_mail($data){
    $mail=$_GET['mail']; //$data->get_param["mail"];
    $course_id=$_GET['course'];
    global $wpdb;

    $user=get_user_by("email",$mail);
    if($user !== false){
        $lp_user=learn_press_get_user( $user->ID );

        if($course_id==NULL){
            $all_courses=ilp_api_get_all_courses($data);
        }else{
            $all_courses=array('courses' => array(array('id' => intval($course_id))));
        }

        $progress=array();
        $i=0;
        if($all_courses!=NULL && $all_courses['courses']!=null){
            foreach($all_courses['courses'] as $course){
                if($lp_user->has_enrolled_course($course['id'])){
                    $lp_course=learn_press_get_course( $course['id'] );
                    $course_data       = $lp_user->get_course_data($course['id']);
                    $course_results    = $course_data->get_results( false );
                    $progress[$i]=array(
                        'id' => $course['id'],
                        'name' => $lp_course->get_title(), //$course['name'],
                        'condition' => $lp_course->get_passing_condition(),
                        'completed' => $course_results['completed_items'],
                        'total' => $course_results['count_items'],
                        'progress' => absint( $course_results['completed_items'] / $course_results['count_items'] * 100 ),
                        'permalink' => $lp_course->get_permalink(),
                    );
                    $i++;
                }
            }
        }
        $result = array(
            'userfound' => true,
            'user_id' => $user->ID,
            'connect' => get_h5p_grades(),
            'courses_progress' => $progress,
            'course_id' => $all_courses,
        );

     function get_h5p_grades(){
    global $wpdb;

    $ID = 1;
    $ID_use = 1;


    $result = $wpdb->prepare('SELECT score FROM mci_h5p_results WHERE id = %d AND user_id = %d', $ID, $ID_use);
    $result->execute();
    $donnees = $result->fetch();
    return $donnees;
}