my-custom-fields-depends-example.php

<?php
/**
 * Example of extending a user field to add a depends
 *
 * This recipe assumes a checkbox field with the name my_checkbox was created.
 * This recipe assumes a textarea field with the name my_textarea was created.
 *
 * 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_pmpro_user_fields_add_depends() {
	global $pmpro_user_fields;

	// bail if Paid Memberships Pro is not active
	if ( ! function_exists( 'pmpro_add_user_field' ) ) {
		return;
	}

	// loop through the fields and add the depends
	foreach ( $pmpro_user_fields as $field_group => $fields ) {
		foreach ( $fields as $field ) {
			if ( 'my_textarea' === $field->name ) {
				$field->depends = array(
					array(
						'id'    => 'my_checkbox',
						'value' => true,
					),
				);
			}
		}
	}
}
add_action( 'init', 'my_pmpro_user_fields_add_depends' );