title: Yii2 : Checkbox rules not working at signup for terms and conditions
body: <p>On signup, I need a certain message, but for some reason, it fails to show my message.</p>
  
  <p>please help</p>
  
  <p>I have the following rules:</p>
  
  <pre><code>['acordul_tc', 'required', 'on' =&gt; ['register']],
  ['acordul_tc', 'integer', 'max' =&gt; 1, 'message' =&gt; 'my test message'],
  </code></pre>
  
  <p>and the html:</p>
  
  <pre><code>&lt;div style='position:relative; float:left; padding:5px;'&gt;
  &lt;div style='float:left; padding:5px;'&gt;
      &lt;?php
          echo $form-&gt;field($model, 'acordul_tc', 
          ['options' =&gt; ['tag' =&gt; 'span',], 
          'template' =&gt; "{input}"])-&gt;checkbox(['checked' =&gt; false]);
      ?&gt;
  &lt;/div&gt;
  &lt;div style='float:left; padding:5px;'&gt;
      &lt;?php
          echo \Yii::t('user', 'acordul_tc_start') . 
          Html::a(Yii::t('diverse', 'Termenii si Conditiile'), 
                 ['site/terms-and-conditions']) . 
              \Yii::t('user', 'acordul_tc_end');
      ?&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  &lt;div class="col-lg-12"&gt;
  &lt;?php
      echo $form-&gt;field($model, 'acordul_tc', 
           ['template' =&gt; "{error}"])
           -&gt;error();
  ?&gt;
  </code></pre>
  
  <p></p>