Here is current mirrorlist:
[root@adam-pc adam]# cat /etc/pacman.d/mirrorlist
#
# KaOS repository mirrorlist
#
# Brazil
#Server = http://www.lasca.ic.unicamp.br/pub/kaos/$repo
#Server = ftp://ftp.lasca.ic.unicamp.br/pub/kaos/$repo
# Czech Republic
Server = http://193.86.184.157/kaos/$repo
# Germany
Server = http://mirror6.layerjet.com/kaos/$repo
# France
Server = http://kaos.youm.org/$repo
# Netherlands
Server = http://nyxi.eu/mirrors/kaos/$repo
# South-Africa
Server = http://ftp.wa.co.za/pub/kaos/$repo
# United States
Server = http://mirror.dacentec.com/kaosx/$repo
Server = http://kaosx.tk/repo/$repo
Server = https://kaosx.us/repo/$repo
I did pacman -Syy and error 403 persists. It looks like my mirror refuses access, but manual test in browser seems functional. Maybe it tries to access URL, that is not there.