Web API call works in desktop, but when published Im unable to refresh

Hi,

I have a report that works fine in Power BI desktop (retrieving JSON data from a public web API using Json.Document(Web.Contents()) ). However, when I publish I get the error that "Your data source can't be refreshed because the credentials are invalid". Full query below. URLs changed for privacy:

let

    AuthKey = GetSessionId(),
    url = "https://publicapi.com",
    body = "{typeName: 'Project',
        fields: ['name', 'TrackStatus.name', 'BudgetStatus.name'],
        where: {
	    _type: 'Compare',
	    leftExpression: {fieldName: 'State'},
	    operator: 'Equal',
	    rightExpression: {value: 'Active'}
	},
    }",

    Source = Json.Document(Web.Contents(url,[          
         Headers = [#"Authorization"= AuthKey ,
                    #"Content-Type"="application/json"],
         Content = Text.ToBinary(body) 
         ]   
    )),
    entities = Source[entities],
   in
    entities

The GetSessionId() method refers to another query to another web api to receive the session id

let
    Source = Json.Document(Web.Contents("https://publicapi.com",[            
         Headers = [#"Content-Type"="application/json"],
         Content = Text.ToBinary("{userName:'<user>',password:'<pass>'}") 
         ]   
    )),
    sessionId = "Session " & Source[sessionId]
in
    sessionId