/**
 * Callback function for the 'webmention_post_id' filter.
 *
 * @param mixed $id 
 * @param string $url 
 * @return mixed The filtered value.
 */
function my_webmention_post_id_callback( $id, string $url ) {
    // Your code here.
    return $id;
}
add_filter( 'webmention_post_id', 'my_webmention_post_id_callback', 10, 2 );

apply_filters( 'webmention_post_id', $id, $url )

apply_filters( 'webmention_post_id', get_option( 'webmention_home_mentions' ), $url )

apply_filters( 'webmention_post_id', $id, $url )