Cacher is the code snippet organizer for pro developers

<?php
/**
 ** displays alternate html when no posts are found
 **/
add_filter( 'facetwp_template_html', function(  $output, $class ) {
    if ( $class->query->found_posts < 1 ) {
        $output = 'No posts found';
        // add below if you want to output any facets from the filters
        // change my_facet_name to the name of your facet
        if ( isset( FWP()->facet->facets['my_facet_name'] ) ) {
            $keywords = FWP()->facet->facets['my_facet_name']['selected_values'];
            $keywords = is_array( $keywords ) ? implode( ' ', $keywords ) : $keywords;
        }
        if ( !empty( $keywords ) ) {
            $output .= ' for ' . $keywords;
        }
    }
    return $output;
}, 10, 2);