[RuntimeException]
Could not start session because headers have already been sent. "/home/m/mtk42/mupk42/public_html/api/v1/list_categories/xml.php":1. (0)
/home/m/mtk42/mupk42/public_html/bitrix/modules/main/lib/session/session.php:144
#0: Bitrix\Main\Session\Session->start()
/home/m/mtk42/mupk42/public_html/bitrix/modules/main/lib/session/kernelsessionproxy.php:47
#1: Bitrix\Main\Session\KernelSessionProxy->start()
/home/m/mtk42/mupk42/public_html/bitrix/modules/main/include.php:168
#2: require_once(string)
/home/m/mtk42/mupk42/public_html/bitrix/modules/main/include/prolog_before.php:19
#3: require(string)
/home/m/mtk42/mupk42/public_html/api/v1/list_categories/xml.php:21
#4: require(string)
/home/m/mtk42/mupk42/public_html/api/v1/list_categories/index.php:2
----------