(415): Unsupported Media Type - Json

EduardoRocha96  - Json.FromValue is incorrect.  You need to define a text string and convert it to a binary file type.

let
    url = "https://merchant-api.ifood.com.br/authentication/v1.0/oauth/token",
    #"Client Id" = "c9daf25e-6b3d-4e7b-9eed-36792df10be9",
    #"Client Secret" = "l4jkpmdp4axfyn60olr8685s85f8yvq3hugf5h1jztq65tjx8mbg209ljcj4bjxd5vg13s1k21gm869oyaa5y509az47ll8buy3",
    body = "grantType=client_credentials&clientId=" & #"Client Id" & "&clientSecret=" & #"Client Secret",
    #"body to binary" = Text.ToBinary( body ),
    response = Web.Contents(
            url,
            [ 
                Headers = [ #"Content-Type" = "application/x-www-form-urlencoded" ],
                Content = #"body to binary"
            ]
        ),
    open = Json.Document( response ),
    token = open[accessToken]
in
    token