May I ask have you tried using a different Web browser, or tried clearing your Web browser cache?
How about using a Private window (Incognito mode) or a VPN connection if possible?
Is it the same behaviour on your mobile phone (4G LTE, mobile data, cellular)?
Before moving to Cloudflare, was your domain working over HTTPS connection?
Nevertheless, usually steps for troubleshooting the SSL:
Use the “Pause Cloudflare on Site” option from the Overview tab for your domain at dash.cloudflare.com .
The link is in the lower right corner of that page.
Give it five minutes to take effect, then make sure site is working as expected with HTTPS without any error
Check with your hosting provider / Plesk panel / cPanel AutoSSL / Let’s Encrypt / ACME / Certbot and manually click to renew it
Only then, when your website responds over HTTPS, you should un-pause Cloudflare and double-check your SSL/TLS setting to make sure it’s set to Full (Strict).
To understand which SSL encryption mode you should select depending on the setup and your origin SSL certificate (if you have got any, or even invalid one?), please use below article for more information:
You’d experience issues such as mixed content or redirection loop.
Why not? Is this option disabled for you? Could be if you’re under a Cloudflare partner and for some strange reason they disabled it
Otherwise, again, to use Full (strict) you need a valid SSL certificate installed on your origin host/server first.
Since your Website is some kind of a chat, I’d suggest cross-checking the WebSocket as well if you’re using them and having some issue with HTTP<->HTTPS and WS<->WSS connection(s).
to use Full (strict) you need a valid SSL certificate installed on your origin host/server first.
How to do this, maybe i do not have certificate so i can not set it in full/strict mode.
In case if you don’t have one, then you can create and generate one at Cloudflare dashboard for your domain, therefrom install it to your web server using the instructions below and use Cloudflare Origin CA certificate:
It this option works best for you, and you don’t see any error or issue on your Website or for your end-visitors so far, yes.
I understand. Sometimes it can get complex where it doesn’t need nor have to be
No worries. Thank you for asking questions to determine what’s the best case at the current moment for you