It seems that the certificate chain is not complete on android, linux and iphone devices. Only windows works.
Also internet filters not running on windows block the SSL connection.
Online SSL testing tools don’t work on free hosting because they get blocked by this:
As I shared in my screenshot, your certificate is working perfectly fine for me, and as others have said, it’s working fine for them to. The issue is your browser/device, it’s not the certificate or your website. The VPN suggestion lets us confirm that, and gets you access to your site.
The free.nf domain appears to be blocked by some providers. It’s notably listed in IBM’s X-Force Exchange as being a phishing URL. This data source is consumed by some DNS resolvers, such as Quad9, for their own blocklists.
I’ve been trying to get the free.nf domain delisted from there, but unsuccessfully so far.
In the mean time, you could try reporting this issue to KPN and see if they can push the issue from their end. Alternatively, you could consider moving your website to a different subdomain.
