FacetWP – append character to each value

<?php

function fwp_append_char( $params, $class ) {
    if ( 'YOUR_FACET_NAME' == $params['facet_name'] ) {
            $params['facet_display_value'] .= ' €';
        }
    }
    return $params;
}
add_filter( 'facetwp_index_row', 'fwp_append_char', 10, 2 );