How do I fix a 502 Bad Gateway Certificate verify failed: unable to get local issuer certificate

502 is an error related to inter-server communications. It usually has nothing to do with your system (I mean, it's possible that bad cached data or bad DNS settings could be involved, but not usually...it's easy enough to clear your caches in Safari or just force an uncached page reload).

The most common cause of 502 is something going wrong between a proxy server and the upstream content server it is trying to browse to...are you behind a web proxy when this happens - either your own or one at your place of work?

OK, well that simplifies things at least. What does your home network setup look like? Does your ISP just provide a cable modem or something like that, or is it also a router that provides your Wifi?

If just a modem and you have your own Wifi router, what brand? I'm assuming you didn't do some kind of custom install and replace the firmware - everything is stock equipment and you just set it up according to the user guide (setting passwords and so on)?

Does that 502 error happen with all sites, most sites, or just a specific set of sites?