In minecraft I was making a map and I type tellraw @a[r=500]

as a test and it said an error message I tried it in a lot of other ways and it still doesn't work saying: "Invalid json: malformed JSON at line 1 column 2" or "Invalid json: malformed JSON at line 1 column 3". Really a lot of commands aren't working right but this was the only one I needed.
Also I changed my minecraft username but I need a way to change it on here.