Update a post custom form & Paypal

You can use the gform_paypal_fulfillment hook to run actions when a PayPal transaction is completed. http://www.gravityhelp.com/documentation/page/Gform_paypal_fulfillment

You can write a function that updates a post and adds the information to the custom field. We'll need more information from you to be able to give you more specific assistance. The code will look something like this:

[php]
add_action("gform_paypal_fulfillment", "update_custom_field", 10, 4);
function update_custom_field($entry, $config, $transaction_id, $amount) {
    $post_id = $entry['post_id'];
    // define your meta key name here
    $meta_key = 'custom_field_name';
    // write the transaction ID to the meta key
    update_post_meta($post_id, $meta_key, $transaction_id);
}

Are you saying you want to update a post which already exists, after getting a PayPal payment, with the new expiration date or how long the post should stay visible? The post (ad) already exists, and you are giving the opportunity to run the ad longer, by making a PayPal payment?

If that is true, I don't think it will be too difficult. You can pre-populate the form as you are doing with the query string link and the post_id in it. That will get you the post_id. Then, use the field value where that is stored to update the post meta:

[php]
$post_id = $entry['field_id_where_post_id_is_stored'];
$expires = 'whatever your expiration date is';
update_post_meta($post_id, ' is_featured', $expires);

You will have to figure out how to calculate the expiration date, then use that in your custom post template to not show posts with expired dates in the meta key.

You're welcome. If you get stuck, let us know and we will try to help.