Shows how to add custom variables to a memberpress signup form.

custom_signup.php

<?php
/*
Plugin Name: MemberPress Custom Membership Signup
Plugin URI: http://memberpress.com
Description: Adds some custom fields to the MemberPress signup process 
Version: 1.0.0
Author: MemberPress
Author URI: http://memberpress.com
Text Domain: memberpress
*/

if(!defined('ABSPATH')) {die('You are not allowed to call this page directly.');}

include_once( ABSPATH . 'wp-admin/includes/plugin.php' );
if( is_plugin_active('memberpress/memberpress.php') ) {
  class MemberpressCustomSignup {
    public function __construct() {
      $this->load_hooks();
    }

    public function load_hooks() {
      add_action('mepr-user-signup-fields', array($this, 'display_signup_fields'));
      add_filter('mepr-validate-signup', array($this, 'validate_signup_form'));
    }
    
    // This is where you put the html for the signup fields ...
    // I prefer to just break out of the php block like so
    public function display_signup_fields() {
      ?>
        <div class="mepr_signup_table_row">
          <label for="company"><?php _e('Company:'); ?></label>
          <input type="text" name="company" id="company" value="" />
        </div>
      <?php
    }
    
    // This get's called after the post request ...
    // the $error parameter is an array ... all you have to do to throw an error is
    // add an error message to the $errors array and return it like so
    public function validate_signup_form($errors) {
      if(empty($_POST['company']))
        $errors = __('Company can\'t be blank.');

      return $errors;
    }
  }

  // Load hooks, etc.
  new MemberPressCustomSignup();
}