Which 400 codes? There are more than 20. They mostly suggest a problem at the client end, and are often security related.
Your ISP, Browser, or possibly operating system tightening up security may explain part or all of it.
For over a decade, it's been recognised that websites that don't have a security certificate are risky, for several reasons. As none of them are instantly painful, they've been allowed to chug along. But they're a weakness in the defences, for example they make it much easier for the bad guys to put up a website that spoofs your bank and get away with it for longer than is safe. And sloppy computer security of any sort is a strong hint to hackers, that the site is part of a sloppy security community, likely to provide other loop-holes/
Run a mile from any site on the internet that collects personal data or collects money that doesn't have a certificate. You do check security certificates, right? Of course we don't, here's a popular website:
![lathesukcert.jpg lathesukcert.jpg](data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==)
Note the padlock symbol crossed with a red-line in the address box, and that the address doesn't mention https:
The red line is a warning to security conscious users to beware. The site is safe enough provided the user is careful, doesn't give anything away, and has moderately good security himself.
However, internet providers have been taking an increasingly hard line with websites that don't have a security certificate. ISPs refusing to host new ones; browsers issuing loud warnings, and more recently refusing to connect at all. (Unless the user goes into Settings and deliberately disables the security check.) After many warnings the idea is to force security on anyone who hasn't voluntarily plugged the loophole, and to ensure innocent users know something is wrong.
That two devices are blocked suggests a common reason. Might be the Router. At home, most smart phones connect to the internet using WiFi rather than the mobile network. If the router checks for certificates, everything that connects via the router will fail. Possibly the ISP has tightened up the router in one of the periodic upgrades. Or, the router has been corrupted by a glitch. Some strange faults can be fixed by powering off the router for several minutes, or forcing a full reset. ('Have you tried switching it off and on again' is good advice!)
Could be wrong. More information the better when there a multiple causes, or something complicated going on : exactly which codes and error messages, which browser and version, which operating system and version, examples of websites that work and sites that don't.
Dave
Edited By SillyOldDuffer on 17/03/2023 13:14:43