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Fatal error: Uncaught Mpdf\MpdfException: Data has already been sent to output (/var/www/html/index.php at line 14), unable to output PDF file in /var/www/html/vendor/mpdf/mpdf/src/Mpdf.php:9412 Stack trace: #0 /var/www/html/controller/ReportGenerator.class.php(78): Mpdf\Mpdf->Output() #1 /var/www/html/index.php(18): ReportGenerator->output() #2 {main} thrown in /var/www/html/vendor/mpdf/mpdf/src/Mpdf.php on line 9412