Cloudflare error 526 – Invalid SSL certificate

We have put cloudflare SSL/TSL Full(strict) mode and tested our Live environment for about 1hr. Initially it gave 526 error but then it worked without error.
After testing we have put SSL/TSL full mode again.
And then next day we have put cloudflare SSL/TSL Full(strict) mode again and this time error 526 frequently.
We want to set cloudflare SSL/TSL Full(strict) mode but we cannot because of this error.

I have the same issue everytime the server needs to update ssl

That error is quite clear: The SSL certificate you have on your server is not valid for your domain.

To display the origin certificate (assuming one is installed), replace 203.0.113.34 below with the actual IP address of your origin web server and replace www.example.com with your domain and host name:

curl -svo /dev/null https://www.example.com --connect-to ::203.0.113.34 2>&1 | egrep -v "^{.*$|^}.*$|^* http.*$"

I check this command, but don’t have solutions.

Any output from it?