I see, but the first example option having no code still makes it harder to translate and show the user, so my vote is for the option with a code and message in the json.

Message straight on the body is the worst possible response for an error here, it is bad design to straight up show the error from the back end to the user, usually it needs translation and/or adaptation due to message size on the front-end to show properly, and applying those on top of a message will make it stop working as soon as anyone in the backend decide to change a dot or comma anywhere. It is a bad idea to let the backend make direct impact in the front when you can because backend devs won’t even know what impact they are causing until later in testing and it will be harder to trace back and fix.

IMO you need at least a json with code and message, the front will ignore the message for everything but testing and use the code to match a translation file that will get the proper message, making it easy to translate and change as needed without having to rebuild the whole backend along with front changes. You may also have an extra parameter there in some cases when you want to return where more specifically the error occurred or an array of errors. Status usually not needed as you can get those from the http code itself.

I saw this exact popup yesterday, I remember seeing something similar to it before but it has been quite a while. The thing is, this single popup broke my computer entirely, I was playing a game and it jumped in front of the game, immediately stole the games inputs and I couldn’t even pause it. Then clicking don’t switch did absolutely nothing and the popup remained there, and any attempt to forcefully close the popup failed. Also, I was streaming at the time to my tv, and attempting to use any system related screen is blocked (and this popup counts as a system settings screen!), So it just crashed the entire thing while I was trying to dismiss or close it. I was stuck and couldn’t even reboot, had to hold the button and lose any progress I had in the game.

So yeah, I would be very interested in not letting this happen again as well.