Whoooh! That’s a tall order.
First you must parse/tokenize your json to get your variables broken down as separate entities. This should be relatively easy as there are a ton of json parsers around the internet.
Next you’ll have your values in “7B 22 4D …” format. At this point you should know what is the character encoding is (UTF-8, ASCII). Check your wss server documentation to figure how to reverse the encoding as it might be custom.
I strongly advice against doing this in blueprints. There are tons of readily available c++ libraries you can integrate in your project. (Your server probably comes with some too for decoding)