Accessing Planday API with M

Hi,

I am trying to access the APIs of Planday (explained in detail here) from Power Query, but I have some issues authenticating to get the access token.

The relevant info about the API:

Before you can make calls to the API resources, you first need to obtain an Access Token by exchanging the Refresh Token from the previous sections for an Access Token. To do this, you need to make a POST request using any tool you want that can make HTTP calls (curl, postman, etc.) The request is as follows (replace CLIENT_ID and TOKEN with appropriate values):

POST https://id.planday.com/connect/token Request Headers: Content-Type: application/x-www-form-urlencoded Request Body: client_id=CLIENT_ID&grant_type=refresh_token&refresh_token=TOKEN

My query attempt that receives a 400 - Bad attempt error:

let
url = "https://id.planday.com/connect/token",
body = "client_id=<MyClientId>,grant_type=refresh_token,refresh_token=<MyRefreshToken>",
Source =
Json.Document(Web.Contents(url, [Headers=[#"Content-Type"="application/x-www-form-urlencoded"],Content=Text.ToBinary(body)]))
in
Source

My knowledge of M is quite limited, so my attempt may be way off, but I have tried copying another query that works in a similar case with other APIs. 

If any of you are able to spot an error or rewrite the entire query for it to work - it would be highly appreciated!

Thanks!