I changed value in /var/www/nextcloud/.user.ini and it works

user.ini file :

mbstring.func_overload=0
always_populate_raw_post_data=-1
default_charset='UTF-8'
output_buffering=0

mbstring.func_overload=0
always_populate_raw_post_data=-1
default_charset=’UTF-8′

output_buffering=’Off’

output_buffering=0