Can't use get_post_meta() inside a hook function

Question

I'm using {status}_{post_type} hook and need to grab a custom meta from the post:

add_action( 'pending_book', function( $post_id, $post ) {
    $foo = get_post_meta($post_id, 'book_author', true);
    var_dump($foo);
}, 99, 2 );

But it return string(0) ""

The post was generated in frontend, using GravityForms.

What can I do?

Answer 1

Here is the solution: GravityForm hook

add_action( 'gform_after_submission_13', function( $entry, $form ) {
    $foo = get_post_meta($entry['post_id'], 'book_author', true);
    var_dump($foo);
}, 10, 2 );

Where 13 is the ID of form.

More info here: https://www.gravityhelp.com/documentation/article/gform_after_submission/