FacetWP - translate strings using gettext

test.php

<?php

add_filter( 'gettext', function( $translated_text, $text, $domain ) {
    if ( 'fwp' == $domain ) {
        if ( 'Start typing...' == $translated_text ) {
            $translated_text = 'The new placeholder';
        }
    }
    return $translated_text;
}, 10, 3 );