This recipe creates an additional Terms and Conditions checkbox field.

my-pmpro-terms-and-conditions-checkbox.php

<?php
/**
 * This recipe creates an additional Terms and Conditions check field.
 *
 * @requires Register Helper Add On
 * @link https://www.paidmembershipspro.com/add-ons/pmpro-register-helper-add-checkout-and-profile-fields/
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function my_pmprorh_init_example_fields() {
	// don't break if Register Helper is not loaded
	if ( ! function_exists( 'pmprorh_add_registration_field' ) ) {
		return false;
	}
	// define the fields
	$fields   = array();
	$fields[] = new PMProRH_Field(
		'por_favor_confirme', // input name, will also be used as meta key
		'checkbox', // type of field
		array(
			'label'    => 'Por favor, confirme',
			'text'     => 'Acepto las siguientes condiciones: Libero a la Asociación Centro de Yoga Sivananda Vedanta y a sus profesores de toda responsabilidad en caso de sufrir cualquier daño . Afirmo estar en buena salud y no padecer ninguna enfermedad grave . Asimismo, estoy informado / a de que practico todos los ejercicios bajo mi propio riesgo y propia responsabilidad, y que puedo abstenerme de realizar uno o varios ejercicios en cualquier momento . ', // custom field label
			'required' => true, // make this field required
			'profile'  => 'admin', // show only to admins on the profile page
		)
	);
	foreach ( $fields as $field ) {
		pmprorh_add_registration_field(
			'before_submit_button', // location on checkout page  //before_submit_button checkout_boxes
			$field            // PMProRH_Field object
		);
	}
	// that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action( 'init', 'my_pmprorh_init_example_fields' );