FPDF error: Some data has already been output, can't send PDF

if you're code outputs notices/warnings before the PDF generation, try turning them off. `error_reporting(0)`. Then work on the warnings there-after

I used the following and it worked for me

require_once ('pdf/fpdf.php');

$pdf = new FPDF();
$pdf->AddPage();
$pdf->SetFont('Arial','B',16);
$pdf->Cell(40,10,'Hello World!');
$pdf->Output(F,'/var/www/html/PATH/filename.pdf');
ob_end_flush();

Add to the beginning of the script

ob_start();
require ('fpdf.php');

and at the end, after `output()`

ob_end_flush();

It worked for me! =)

Fatal error: Uncaught exception 'Exception' with message 'FPDF error: Some data has already been output, can't send PDF file (output started at /home/asri123/public_html/bill/invoice/invoice.php:743)' in /home/asri123/public_html/bill/invoice/fpdf.php:271 Stack trace: #0 /home/asri123/public_html/bill/invoice/fpdf.php(1052): FPDF->Error('Some data has a...') #1 /home/asri123/public_html/bill/invoice/fpdf.php(1012): FPDF->_checkoutput() #2 /home/asri123/public_html/bill/invoice/mirasbill.php(262): FPDF->Output('MSFS/2018-19/76...', 'D') #3 {main} thrown in /home/asri123/public_html/bill/invoice/fpdf.php on line 271

Even a single space in the included php files causes that warning. There shouldn't be any output in any way.

Another answer that nobody else has posted here... **Double-check the encoding of your PHP file** and make sure that it's not something other than UTF-8. The wrong code editor (or FTP upload?) can mess with the file's encoding in which case none of the other fixes mentioned in this thread will help.