Many hosts require the SSL be installed on their end.. making the one cloudflare provides useless.
I would suggest going using a plugin like Better Search and Replace to fix any references to the insecure version of the URL after activating the SSL on the hosts side. If you find that some pages are still showing the “insecure content” error after using Better Search Replace then you will need to go into the code for those page or the page editor of your theme and update the references manually by changing the images/urls/etc so that they are linking to https.
Hope this helps once you get your SSL working kindly tag the thread as resolved.