I might have an idea of the error, T12.
JSON is a standard data interchange format that stores data structures. It is used for transmitting data between web applications or servers, too.
This error has several triggering factors. One of them is the sudden interruption of your internet connection. Cache can cause this issue when they're piled up on your browser, too.
Usually, it is fixed by keeping a stable internet connection and refreshing your browser (F5). If the same thing happens, we can do a few troubleshooting steps.
- Open private window and access your liability account. It uses but doesn't store cache.
- If that goes through smoothly, you can go back to your regular browser and clear the cache.
- Other supported browsers are good alternatives, too. Cache differs from each browser.
Give it a try and I'll get back to you if you need more help.