How to Authenticate to a REST API with basic Authentication in Power BI Blank Query

I have a need to access a REST API (JSON) to access data in CSV format.

https://apiURL/apps/api/batch-query/

With Header as follows:

Authorization = "Basic <encoded username : password>"

Content-Type = "application/json"

My code is as follows:

let
 source = #!"Json.Document(Web.Contents(""https://apiURL.com/apps/api/batch- query/"", [#Authentication=""Basic <encoded username : password""]))"
in
 source

I receive error saying the header authorization can not be used. Most examples I have seen are using token/key, this API does not have that capability. Using a REST Client the call works just fine.

Is there a simple way to make a connection to the API with basic Auth, I need to do a POST, GET, GET (each requests will use a value from the previous request.

Thanks