HTTPS stop to work suddenly

Can you post a screenshot of that section of your SSL/TLS settings page?

Did you buy a $5/month Dedicated certificate? It would be listed a bit farther down the page. It would be in the Edge Certificates section. Can you post a screen shot of that section?

No, it’s a free plan

That’s broken. There should be a certificate in that section. Go to that “Flexible” setting and turn it Off. Wait 10 minutes, then turn it back on to Flexible. The Status should show something after that.

If nothing shows up, open a support ticket: Login & go to https://dash.cloudflare.com/?account=support

Create a new account and try to set it there.