Display Line chart with data retrieved from MySQL Database

I am using a template built on Bootstrap 4 & 5. There is a line chart already featured, with hardcoded values being displayed.

Hardcoded values:

<div class="col-lg-3 col-md-6 col-sm-6">
                    <div class="card overflowhidden number-chart">
                        <div class="body">
                            <div class="number">
                                <h6>SALES</h6>
                                <span>$500</span>
                            </div>
                            <small class="text-muted">19% compared to last week</small>
                        </div>
                        <div class="sparkline" data-type="line" data-spot-Radius="0" data-offset="90" data-width="100%" data-height="50px"
                        data-line-Width="1" data-line-Color="#604a7b" data-fill-Color="#a092b0">**1,4,2,3,6,2**</div>
                    </div>
                </div>

And it looks like this visually:

enter image description here

Now, I have a MySQL database and I want to retrieve the data to display it on the line chart.

I removed the hardcoded values and added the MySQL query. Please tell me what I’m doing wrong because the retrieved data is not being displayed. My DB connection is ok.

<div class="row clearfix">
            <div class="col-lg-3 col-md-6 col-sm-6">
                    <div class="card overflowhidden number-chart">
                        <div class="body">
                            <div class="number">
                                <h6>Water Level</h6>
                                <span><p></p><p></p></span>
                            </div>
                            <small class="text-muted">Last 2 Hours</small>
                        </div>
                        <div class="sparkline" data-type="line" data-spot-Radius="0" data-offset="90" data-width="100%" data-height="50px"
                        data-line-Width="1" data-line-Color="#604a7b"  data-fill-Color="#a092b0">
                        **<?php
                        $sql2 = "SELECT water_level as water_level FROM `tbl_water_level` WHERE `date` > SUBDATE( NOW(), INTERVAL 2 HOUR)";
                            $result2 = mysqli_query($conn, $sql2);
                            $data = '';
                            while($data=mysqli_fetch_array($result2)){
                                echo '.$row["water_level"].'; 
                            }
                            
                        ?>**
                        </div>
                    </div>
                </div>
        </div>