$re = '/Purchase Order:\s*([A-Z\d-]+)\s*Invoice/m';
$str = 'SVC,PRO,WL CHRGE CASE-LKKT,CI/AR Purchase Order: CLC-GT-103782 Invoice AE78060885/14.03.2022 Country of Origin: VN';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php