The following websites can't be visited by using HTTPS ("Unable to connect" Error):
https://repo.pureos.net/pureos/pool/main/
https://repo.puri.sm/pureos/pool/main/p/pureos-archive-keyring/pureos-archive-keyring_2016.09_all.deb
https://master.pureos.net
fix:
support HTTPS on all subdomains related to purism/pureos.