В документации прописано вот что:
-H "accept: application/json; charset=utf-8"
-H "Content-Type: application/json"
-d "{\"Login\":\"demo\",\"Password\":\"demo\",\"TimeZoneOlsonId\":\"Europe/Moscow\",\"CultureName\":\"ru-ru\",\"UiCultureName\":\"ru-ru\"}"
let
data = Json.FromValue([Login="demo",Password="demo",TimeZoneOlsonId="Europe/Moscow",CultureName="ru-ru",UiCultureName="ru-ru"]),
headers = [#"accept"="application/json; charset=utf-8", #"Content-Type"="application/json"],
web = Web.Contents("
https://url.ru", [ Content = data, Headers = headers, ManualStatusHandling = {404, 400}]),
result = Json.Document(web)
in result