I have a single checkbox field (not checkboxes) in a custom form, when I try to get the value in a submit handler the value is always 0 whether it’s selected or not.

  /**    * {@inheritdoc}    */   public function buildForm(array $form, FormStateInterface $form_state) {      $form['item_specifics'] = [       '#type' => 'checkbox',       '#title' => t('Sync item specifics'),       '#attributes' => [         //define static name and id so we can easier select it         // 'id' => 'select-colour',         'name' => 'field_item_specifics',       ]     ];      $form['fieldset_item_specifics'] = [       '#type' => 'fieldset',       '#title' => $this->t('Item Specifics'),       '#attributes' => [         //define static name and id so we can easier select it         'class' => ['form-wrapper', 'js-form-wrapper'],       ],       '#states' => [         //show this textfield only if the radio 'other' is selected above         'visible' => [           //don't mistake :input for the type of field. You'll always use           //:input here, no matter whether your source is a select, radio or checkbox element.           ':input[name="field_item_specifics"]' => ['checked' => TRUE],         ],       ],     ];      $form['submit'] = [       '#type' => 'submit',       '#value' => $this->t('Sync'),     ];      return $form;   }      /**    * {@inheritdoc}    */   public function submitForm(array &$form, FormStateInterface $form_state) {      dpm($form_state->getValue('item_specifics'));    }   } 

The output of dpm() is always 0, if I dpm() form state then the values array always has the checkbox value as 0.