function advanced_custom_field_excerpt() {
	global $post;

// check if the flexible content field has rows of data
if( have_rows('post_flexible_content') ):

     // loop through the rows of data
    while ( have_rows('post_flexible_content') ) : the_row();

	$text = get_sub_field('flexible_text_editor');
	if ( '' != $text ) {
		$text = strip_shortcodes( $text );
		$text = apply_filters('the_content', $text);
		$text = str_replace(']]>', ']]>', $text);
		$excerpt_length =30; // 30 words
		$excerpt_more = apply_filters('excerpt_more', ' ' . '[...]');
		$text = wp_trim_words( $text, $excerpt_length, $excerpt_more );
		break;
	}

    endwhile;

else :

    // no layouts found

endif;

	return apply_filters('the_excerpt', $text);
}
add_shortcode("flexible-excerpt", "advanced_custom_field_excerpt");