Error 526 error with valid certificate

Hello, I get this error on the website https://mattesglobaltrading.com even though the webhost is saying that I have an active ssl certificate that is fine.

They said to switch to these settings which I did:
Always Use HTTPS
Automatic HTTPS Rewrites
SSL - Flexible

Do I need to wait for the changes to take effect or they are instant?
The issue still is not resolved.

Any ideas what else can I do?

Hello,
Such changes are instant.
Did you try to use the “Full” SSL Mode?
See the following KB: