how to fix https error?
You probably should look at Magento's documentation on how to setup SSL in it since there might be a specific way to set it up. https://magento.com/
You might find your answer at one of these two sites:
Did you use Let's Encrypt? What OS are you running?
Your SSL is not working… even 'http' comes up as "not secure" in my bowser (no lock icon).