Add new custom fields to Advanced Settings with an array of options. Supports 'text','select', and 'textarea' as field_types.

my_pmpro_custom_advanced_options.php

<?php

//Add new custom fields to Advanced Settings with an array of options. Supports 'text','select', and 'textarea' as field_types.
//
//Example:
//
function my_advanced_settings() {
    $custom_fields = array(
        'field1' => array(
            'field_name' => 'test1',
            'field_type' => 'text',
            'label' => 'label1',
            'description' => 'description'
        ) ,
        'field2' => array(
            'field_name' => 'tes22',
            'field_type' => 'text',
            'label' => 'label2',
            'description' => 'another descrioption'
        )
    );

    return $custom_fields;
}
add_filter('pmpro_custom_advanced_settings','my_advanced_settings');
//
//Available options:
//
//'field_name' => 'string',  // "id" and "name" attributes
//'field_type' => 'string', // type of field
//'label' => 'string', // field label
//'description' => 'string' // description, shows up under field
//'value' => 'string' //default value
//'options' => array() // array of options (for select fields)
//
//These values can then be used anywhere like so:
//
//$test1 = pmpro_getOption('custom_test1');

I guess we need to change above example code: below is the bit of code used for Paid Memberships Pro - WooCommerce Add On
//existing function
function pmprowoo_custom_settings() {
$fields = array(
'field1' => array(
'field_name' => 'pmprowoo_discounts_on_subscriptions',
'field_type' => 'select',
'label' => 'Apply Member Discounts to WC Subscription Products?',
'value' => 'No',
'options' => array('Yes','No')
)
);
return $fields;
}
add_filter('pmpro_custom_advanced_settings', 'pmprowoo_custom_settings');

So if another plugin author try to use filer pmpro_custom_advanced_settings, their code will be lost.
above function need to rewrite as below:
resource ro follow: http://hookr.io/filters/pmpro_custom_advanced_settings/

function pmprowoo_custom_settings( $fields ) {
$fields['field1'] = array(
'field_name' => 'pmprowoo_discounts_on_subscriptions',
'field_type' => 'select',
'label' => 'Apply Member Discounts to WC Subscription Products?',
'value' => 'No',
'options' => array('Yes','No')
);
return $fields;
}
add_filter('pmpro_custom_advanced_settings', 'pmprowoo_custom_settings', 10,1);

Thanks for the heads up on that. I'll fix up the PMPro WooCommerce one ASAP.