webmention-status.php

<?php

add_action( 'webmention_post_send', function( $response, $source, $target, $post_id ) {

	if ( is_wp_error( $response ) ) {
		// Something went wrong.
		error_log( 'Error trying to send webmention to ' . esc_url_raw( $target ) . ': ' . $response->get_error_message() );
	} else {
		error_log( 'Sent webmention to ' . esc_url_raw( $target ) . '; response code: ' . wp_remote_retrieve_response_code( $response ) );
	}

}, 10, 4 );