<?php

$mes = array();
$total = array();
$cor = array();
$cor[0] = '#ff3300';
$cor[1] = '#0000ff';
$cor[2] = '#006600';
$i = 0;


$servername = "xxx.xxx.x.xx";
$username = "xxxxx";
$password = "xxxxxxx";
$dbname = "xxxxxxx";

$conn = new mysqli($servername, $username, $password, $dbname);
$conn->set_charset('utf8');

$sql = "SELECT MONTH(centrodb.registosagudizacoes.Dataregresso) AS Mes,
       COUNT(NomeUtente) AS Total

FROM centrodb.registosagudizacoes LEFT OUTER JOIN centrodb.ChegAgudizacoes

on centrodb.ChegAgudizacoes.NumRegisto = centrodb.registosagudizacoes.id

WHERE centrodb.registosagudizacoes.Dataregresso IS NOT NULL

GROUP BY MONTH(centrodb.registosagudizacoes.Dataregresso);";

$resultado_cursos = mysqli_query($conn, $result_cursos);

while($rows_cursos = mysqli_fetch_object($resultado_cursos)) {

    $meses = $rows_cursos->Mes;
    $totais = $rows_cursos->Total;
    $mes[$i] = $meses;
    $total[$i] = $total;
$i = $i + 1;
}

?>

<script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
  <script type="text/javascript">
    google.charts.load("current", {packages:['corechart']});
    google.charts.setOnLoadCallback(drawChart);
    function drawChart() {
      var data = google.visualization.arrayToDataTable([
        ["Mês", "Total", { role: "style" } ],
        <?php
          $k = $i;
          for ($i = 0; $i < $k; $i++) {
              ?>
            ['<?php echo $mes[$i] ?>', <?php echo $total[$i] ?>, '<?php echo $cor[$i] ?>' ],
          <?php } ?>
      ]);

      var view = new google.visualization.DataView(data);
      view.setColumns([0, 1,
                       { calc: "stringify",
                         sourceColumn: 1,
                         type: "string",
                         role: "annotation" },
                       2]);

      var options = {
        title: "Density of Precious Metals, in g/cm^3",
        width: 600,
        height: 400,
        bar: {groupWidth: "95%"},
        legend: { position: "none" },
      };
      var chart = new google.visualization.ColumnChart(document.getElementById("columnchart_values"));
      chart.draw(view, options);
  }
  </script>
<div id="columnchart_values" style="width: 900px; height: 300px;"></div>

**Data column(s) for axis #0 cannot be of type string×**