If you're having problems importing a sitemap ("invalid JSON"), try checking it first on the JSONLint validator website at https://jsonlint.com/
It will help you narrow down errors by flagging the line(s). Usually the problem is missing or extra punctuation, or unescaped special characters. As a bonus, it will also "prettify" your JSON and make it easier to read (this is for the humans; WS doesn't really care).
It the site reports "Valid JSON", you can import it into WS.