Making API data sources work in power BI web

[Anonymous]

So I have a table with parameters for changing date ranges in API call.
I followed answers here and other resources and succesfully managed to gather data iteratively. Then I published my report in workplace and detected that it is not possible to refresh dataset. I googled again, stumbled upon reasons and solutions and tried to implement.
So I have upgraded my function-as-parameter so power BI web should be able to validate url:

let
    Source = (param as text) =>
let
    Source = Json.Document(Web.Contents("api_url_part",
    [
        RelativePath="api_url_part" & some_parameter & "api_url_part" & param,
        Query=
        [
            Headers=[Accept="application/json", Authorization="Token xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"]
        ]
    ]
)),
    by_date = Source[by_date],
    #"Converted to Table" = Record.ToTable(by_date),
    #"Expanded Value" = Table.ExpandRecordColumn(#"Converted to Table", "Value", {"session_count", "visitor_count", "desktop_visitors_count", "mobile_visitors_count", "tablet_visitors_count"}, {"session_count", "visitor_count", "desktop_visitors_count", "mobile_visitors_count", "tablet_visitors_count"})
in
    #"Expanded Value"
in
    Source

 My other query that iterates API calls:

let
    step_1 = Date_params[date_param],
    step_2 = List.Transform (step_1, func_p()),
in
    step_3

Before I used Relative Path and Query everything worked on PowerBi desktop, only in web I had problems. Now when I run the second query I get this error message:

Expression.Error: 0 arguments were passed to a function which expects 1.
Details:
    Pattern=
    Arguments=List

If I enter parameter manually, first query is able to retrieve data so it means problem lies in and I need to change second query as well but I cannot figure out how.

Thanks in advance!

[Anonymous]

I made a mistake, I passed underscore as parameter before, this is actual mistake I get:

An error occurred in the ‘’ query. Expression.Error: We cannot convert a value of type Record to type Text.
Details:
    Value=Record
    Type=Type