There is mismatch between HTTPS indicated on the server and client.
This can lead to non working phpMyAdmin or a security risk.
Please fix your server configuration to indicate HTTPS properly.
You are getting the error on login page of phpmyadmin as you are trying to open phpmyadmin url with domain which is https but you are using proxypass for the domain which may be using http url in proxypass.
Solution :
Add following line in your apache virtualhost of the domain
RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
Restart apache
or
If you are using nginx
Add following line in your nginx virtualhost of the domain
proxy_set_header X-Forwarded-Proto https;
Restart nginx
