$re = '/ERRTEXT=\"(?P<ERRTEXT>.+)\",\s+MSGXML/m';
$str = '2021-12-09 09:56:00.998, FACILITY_DETAILS="/v1/facilities/XXXX/arrears", FACILITY_ID="101010/", TIMESTAMP="2021-12-09 03:41:06.768342", CORRELATION="414d51204d425032514d30322020xxxda4b", ORIGIN="FROMORIGIIN", ERRCODE="code":"400",", ERRTEXT="detail":"must be greater than the previously recorded value of 105 days","source":{"pointer":"/data/days_past_due"}}]}", MSGXML="{"errors":[{"id":"3a59de59-8b99-4e4a-abfb-XXXXXX","status":"400","code":"400","title":"days_past_due is invalid","detail":"must be greater than the previously recorded value of 105 days","source":{"pointer":"/data/days_past_due"}}]}"
2021-12-09 09:56:00.998, FACILITY_DETAILS="/v1/facilities/XXXX/arrears", FACILITY_ID="101010/", TIMESTAMP="2021-12-09 03:41:06.768342", CORRELATION="414d51204d425032514d30322020xxxda4b", ORIGIN="FROMORIGIIN", ERRCODE="code":"400",", ERRTEXT="detail":"must be greater than the previously recorded value of 105 days","source":{"pointer":"/data/days_past_due"}}]}", MSGXML="{"errors":[{"id":"3a59de59-8b99-4e4a-abfb-XXXXXX","status":"400","code":"400","title":"days_past_due is invalid","detail":"must be greater than the previously recorded value of 105 days","source":{"pointer":"/data/days_past_due"}}]}"';
preg_match_all($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