How to fix cloudflare error 526

There are a couple of possible problems

1. You have a self-signed certificate
2. Your certificate has expired

Solving problem number 2 should not be hard, Just get a new certificate. However number 1 has a little bit more nuance.

You can either change your certificate to

signed by a certificate authority such as GlobalSign, Verisign, GeoTrust, Comodo, etc and is not a self-signed SSL certificate.

as it says on Cloudflare original post or change your security settings.

Go to

cloudflare page > choose your domain > SSL/TLS> overview

You should se something like this

Make sure you have checked Full option like in the picture bellow

That should fix the issue