To expand a bit more on this (Sandro’s advice I think is spot on):
Visit the SSL dashboard and check your SSL encryption mode setting - it should be to be set to Full (Strict).
If you encounter an error when loading your website with Full (Strict), visit SSL/TLS > Origin Server and follow our deploy an origin CA certificate guide to install a valid certificate on your server - this will allow you to use Full (Strict).
If you cannot install a valid certificate on your origin, you can downgrade your SSL encryption mode to Full as an alternative. As a last resort you can choose Flexible however if you continue to see redirect loops you will need to fix that issue at your origin server. Read our Too Many Redirects guide for further information.