Output an attachment thumbnail

functions.php

<?php

// Add the following into the custom-hooks.php file

add_filter( 'facetwp_builder_item_value', function( $value, $item ) {
    global $post;

    if ( 'attachment' == $item['settings']['name'] ) {
        $value = wp_get_attachment_image( $post->ID );
    }
    return $value;
}, 10, 2 );