The self-signed SSL (secure socket layer) works perfectly for encrypting the data, but it is not signed by a valid CA. This is the reason why, when you access the control panel using the SSL , an SSL warning will be prompted. This KB will teach you how to get rid of the self-signed SSL warning across different types of web browser.
Google Chrome
Solution: Click on 'ADVANCED', then click on 'Proceed to URL.com (Unsafe)' to bypass SSL warning in Chrome.
Mozilla Firefox
Microsoft Edge / Internet Explorer