[RuntimeException] 
Could not start session because headers have already been sent. "/home/w/web4sil9/test.optimed-ufa.ru/public_html/404.php":1. (0)
/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/modules/main/lib/session/session.php:133
#0: Bitrix\Main\Session\Session->start()
	/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/modules/main/lib/session/kernelsessionproxy.php:42
#1: Bitrix\Main\Session\KernelSessionProxy->start()
	/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/modules/main/include.php:166
#2: require_once(string)
	/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/modules/main/include/prolog_before.php:14
#3: require_once(string)
	/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/modules/main/include/prolog.php:10
#4: require_once(string)
	/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/header.php:1
#5: require(string)
	/home/w/web4sil9/test.optimed-ufa.ru/public_html/index.php:2
#6: include_once(string)
	/home/w/web4sil9/web4sil9.beget.tech/public_html/bitrix/modules/main/include/urlrewrite.php:160
#7: include_once(string)
	/home/w/web4sil9/test.optimed-ufa.ru/public_html/404.php:3