views/user/registration/register.php

...
                <?= $form->field($model, 'searchbox')->widget(GooglePlacesAutoComplete::className(),
                    ['options' => [
                        'key' => 'xxxxxxxxxxxxxxxxxxxxxxxxx',
                        'class' => 'form-control',
                        ]
                    ]);
                ?>

                <?= $form->field($model, 'locality')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'administrative_area_level_1')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'administrative_area_level_2')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'country')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'postal_code')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'latitude')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'longitude')->hiddenInput()->label(false); ?>
                <?= $form->field($model, 'place_id')->hiddenInput()->label(false); ?>
...