not able to access $_POST on backend profile update

I’ve found my mistake.
I was hooking twice the same code, one in the ‘edit_user_profile’ and other in ‘edit_user_profile_update’.
I have separated the display code from de update code and now it works like have to:

<?php
function privacity_user_profile_fields() {
    global $user_id;
    $data_consent = get_user_meta($user_id, 'gdpr_user_register_consent', true);
    $data_consent_text="He leído y entendido el cómo se tratarán los datos 
      introducidos durante el registro en esta web.";
    ?>

    <h2 id="privacity">Opciones de privacidad</h2>
    <p>
        <input type="checkbox" name="gdpr_data_consent_field" id="data-consent-field" value="true" <?php echo ($data_consent == 'true') ? 'checked' : '' ?> />
        <label for="data-consent-field"><?php echo $data_consent_text; ?></label>
    </p>
    <?php 
}
add_action('edit_user_profile', 'privacity_user_profile_fields');

function privacity_user_profile_update() {
    global $user_id;
    if ($_POST['gdpr_data_consent_field'] == 'true' ){
        update_user_meta( $user_id, 'gdpr_user_register_consent', 'true' );
    } else {
        update_user_meta( $user_id, 'gdpr_user_register_consent', 'false' );
    }
}
add_action( 'edit_user_profile_update', 'privacity_user_profile_update' );
?>