custom_fields_specific_memberships.php

<?php

function my_pmprorh_init() {
	//don't break if Register Helper is not loaded
	if(!function_exists( "pmprorh_add_registration_field" )) {
		return false;
	}
	
	$fields = array();
	$fields[] = new PMProRH_Field(
        'joint_account_name', // input name, will also be used as meta key
        'text',                         
        array(
            'label'     => 'Joint Account Name',     
            'profile'   => true,    
            'required' => true,
			'levels'	=> array(2,4,16,18)  	// instead of 12, type in the ID of your membership level. More than levels can be added like this, array(1,2,3)
        )
    );
	
	$fields[] = new PMProRH_Field(
		'joint_account_email', // input name, will also be used as meta key
		'text',                         
		array(
			'label'     => 'Joint Account Email',     
			'profile'   => true,    
			'levels'	=> array(2,4,16,18)  	// instead of 12, type in the ID of your membership level. More than levels can be added like this, array(1,2,3)
		)
	);
	
	$fields[] = new PMProRH_Field(
        'birthday',		// input name, will also be used as meta key
        'date',     		// type of field
        array(
            'label' => "Birthday",
            'required'  => true,    // make this field required
            'profile' => true,      // show in user profile
			      'memberslistcsv' => true, //includes in CSV export
			      'levels'	=> array(12)  	// instead of 12, type in the ID of your membership level. More than levels can be added like this, array(1,2,3)
        ));
	
	//add the fields into new checkout_boxes area of the checkout page
  foreach($fields as $field)
		pmprorh_add_registration_field(
			'checkout_boxes',	// location on checkout page
			$field			// PMProRH_Field object
		);
  
	//that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action( "init", "my_pmprorh_init");