Somehow I noticed an error in Opera “Unable to complete secure transaction”, at that time there was version 12.17, which appeared when switching to protected sites starting in an address with https.
The cause of the error is most likely the wrong date and time on the computer, after correctly installing them, the error should disappear.
Also, the error can be eliminated (but not desirable) by disabling certificate verification, for this, in the Opera address bar, type:
Next, in the search bar, find the parameter:
OCSP Validate Certificates
and uncheck the box next to it, then click the “Save” button to apply the changes, close and open Opera.