How to add Custom field in custom portfolio type post

Here is solution to add custom field in your custom portfolio entries, for this you must activate the “custom fields” manually.
Open up portfolio.php OR php function where you registering post type “portfolio. portfolio_register() and search for:

'supports' => array('title','thumbnail','excerpt','editor','comments')

Replace it with

'supports' => array('title','thumbnail','excerpt','editor','comments','custom-fields')