Add a field in a product with AM 4

Hi Alex,
I'm looking for 'How to add a field in a new product'.
I found some solution in forum. But not run.
I try to add a new file named site.inc.php in amember root folder with include code like:

Code:

<?php
add_product_field('field_name', 'Field Name', 'text', "Field Description to appear on product page");
?>

But not run, new product form not having new field.

Can you help me a new solution ?

ok. I just found:
add some code in amember/application/site.php (if not having site.php, just creating)

Code:

Am_Di::getInstance()->productTable->customFields()->add('site_url','Provide URL of your store','text');

if you want add a new field in your billing table ?

Code:

Am_Di::getInstance()->billingPlanTable->customFields()->add('install_theme','Installation theme','text');

Created the site.php and just added the line of code you provided above and didn't see it get added. Is there another step?

sorry. The correct path of site.php is:

amember/application/configs/site.php​

Apparently this covers it. http://www.amember.com/docs/How_to_add_fields_to_a_product