API connection - how to set up automatic refresh?

I designed a dashboard with API as a data source. Let me quote some excerpts:

let

Source = Json.Document(Web.Contents(let today = DateTime.Date(DateTime.LocalNow()) in
"[website]" &
Number.ToText(Date.Year(today)) & "-" &
Text.PadStart(Number.ToText(Date.Month(today)-1),2,"0") & "-" &
Text.PadStart(Number.ToText(Date.Day(today)-1),2,"0") &
"&date-to=" &
Number.ToText(Date.Year(today)) & "-" &
Text.PadStart(Number.ToText(Date.Month(today)),2,"0") & "-" &
Text.PadStart(Number.ToText(Date.Day(today)-1),2,"0") 
in
#Source

It works perfectly when I click on "refresh" in PowerBI Desktop. 

My goal is, however, for the published dashboard to refresh automatically.

It doesn't work. I can't create a dataflow using the script above (message: the source is dynamic). Refreshing the data set gives me an error message too.

Any ideas?