Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/vendor/apy/datagrid-bundle/Grid/Source/Source.php:69)

Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/vendor/apy/datagrid-bundle/Grid/Source/Source.php:69)
when i refresh the page, everything is good however first rendering giving this error.