Connect to a Web Service sending parameters

thanks a lot for your reply!
I manage to make it work in my API using a little bit different code. POST Rest API.
My API needs full URL, and I needed to add timeout parameter. For default, Power BI has a 5 minute timout limit.
The way the timeout duration works is (day,hour,minute,second). So my code below has a 2 hours timeout limit.

for authentication, my API uses login password encoded on base 64.

The command #"Authorization" = "base64-encoded user: password" did not work, so I changed to #"Authorization" = "basic dXNlcjpwYXNzd29yZA==". (there is no space after "user:", but ":" and "p" makes a useless emoji... user:password)

Where "user: password" equals to "dXNlcjpwYXNzd29yZA==", using https://www.base64encode.org/ to encode/decode.

let
url = "http://full.api/url/here/including/all/subfolders",
body = "{""parameter as date"":""2017-10-31"",
""parameter as boolean"":true,
""parameter as number"":3
}",

Source = Json.Document(Web.Contents(url,[
Headers =[#"Content-Type"="application/json", #"Authorization" = "basic "],
Content = Text.ToBinary(body) , Timeout=#duration(0,2,0,0)
]
)),

in
#"Source"