Exception 'Error' with message 'Call to undefined function ot_get_option()'

in /var/www/thegioihanghieu/wp/wp-content/themes/thegioihanghieu/landingpage-full.php:57

Stack trace:
#0 /var/www/thegioihanghieu/wp/wp-includes/template-loader.php(106): include()
#1 /var/www/thegioihanghieu/wp/wp-blog-header.php(19): require_once('/var/www/thegio...')
#2 /var/www/thegioihanghieu/wp/index.php(17): require('/var/www/thegio...')
#3 {main}