可捕获的致命错误：类mysqli_result的对象无法在页面中转换为字符串

public function editDChildVC($vaccineID,$ageID,$dcomment,$currentUserID){
            $session=Modulator::getSession();
            $session->start();
            $currentdrID=$_SESSION['userID'];
            echo $currentUserID;
            $todayDate = date("Y-m-d");
            //To add the reservationID for the vaccine
            $getReserveID = "SELECT ID FROM reservation WHERE date = '$todayDate' AND childID = '$currentUserID'";
            $reserveID = Modulator::getDb()->query($getReserveID);

            //To get the correspnding price for the vaccine
            $getPrice = "SELECT price FROM vaccine WHERE ID = '$vaccineID'";
            $vaccPrice = Modulator::getDb()->query($getPrice);


            $sql="INSERT INTO reservationdetails( amount, comment , ReservationID, vaccineID ) 
            VALUES ( '$vaccPrice',  '$dcomment', '$reserveID', '$vaccineID' )";
            $result = Modulator::getDb()->query($sql);
             if($result = Modulator::getDb()->query($sql)){
                 return true;
             }
             else{
               return false;
            }
        }

I do not get what is the error and I tried to search but they're all on select statements and I am still a beginner and I tried to follow the instructions but failed, VALUES ( '$vaccPrice', '$dcomment', '$reserveID', '$vaccineID' )"; can anyone help?