Function call fails when automatically invoking it, but works when manually invoking

I am trying to create a function that I can upload to the Power BI service to then schedule refreshes.

My current function (with changed references) is called data_labels:

(page as number, access_key as text) as table =>
let
    Source = Json.Document(Web.Contents("https://api.company.com/api/webhooks/labels/?key="& access_key & "&page=" & Number.ToText(page))),    
    results = Source[results],
    #"Converted to Table" = Table.FromList(results, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Expanded Column1" = Table.ExpandRecordColumn(#"Converted to Table", "Column1", {"id", "name", "color"}, {"id", "name", "color"})
in
    #"Expanded Column1"

Which works fine when called in this manner

let
     client_Key    = "xyz987"

    Source = Json.Document(Web.Contents("https://api.company.com/api/webhooks/labels/?key=" & client_Key & "&page=1")),
    RecordCount = Source[count],
    Source2 = {1..Number.RoundUp(RecordCount/10)},

    #"Converted to Table" = Table.FromList(Source2, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Renamed Columns" = Table.RenameColumns(#"Converted to Table",{{"Column1", "Page"}}),
    #"Added Custom" = Table.AddColumn(#"Renamed Columns", "Custom", each data_Labels([Page],client_Key)),
    #"Removed Columns1" = Table.RemoveColumns(#"Added Custom",{"Page"}),
    #"Expanded Custom" = Table.ExpandTableColumn(#"Removed Columns1", "Custom", {"id", "name", "color"}, {"label.id", "label.name", "label.color"}),
in
    #"Expanded Custom"

The metadata returns a record count, which I then use to determine the number of pages required (the API sends back 10 records per page)

When loaded to the service, I can't refresh because the I get the error "Unable to refresh the model because it references an unsupported data source"

I changed the function to:

(page as number, access_key as text) as table =>
let
    Source = Json.Document(Web.Contents("https://api.company.com/api/webhooks/labels/?key=abc123&page=1",
                [
		Query = [key= access_key, page= Number.ToText(page)]
                ])),
    
    results = Source[results],
    #"Converted to Table" = Table.FromList(results, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Expanded Column1" = Table.ExpandRecordColumn(#"Converted to Table", "Column1", {"id", "name", "color"}, {"id", "name", "color"})
in
    #"Expanded Column1"

This works when I manually invoke it, with the key and a page number, but when I invoke it using the code, I get an erro ron the desktop: "Operation is not valid due to the current state of the object"

I cannot work out why it works manually, but not automatically. 

Any help would be greatly appreciated.