Remote API Access to data source sudden errors

I have built a report that pulls some data directly from a REST API.  This API requires authentication, and the following code worked for me to access and pull the data directly into PowerBI:

let
 Source = 
    Json.Document(Web.Contents("https://somesite.com/Web/", 
    [Headers=[
        AccountLoginName="user", 
        AccountPassword="pass", 
        SourceSystemID="123", 
        DomainID="1"],
        RelativePath="path/to/api/endpoint"

However, I loaded the report today to make some modifications, and the following error was presented to me: 

Expression.Error: The 'AccountLoginName' header is only supported when connecting anonymously. These headers can be used with all authentication types: Accept, Accept-Charset, Accept-Encoding, Accept-Language, Cache-Control, Content-Type, If-Modified-Since, Prefer, Referer

Can anyone give me a nudge in the right direction?