load data from url in DAX

I have a database that contains 5 million rows with two columns x and y.
I would like to add a column z whose data is accessible via an API (of the type = apiurl/x ). But the api supports maximum 50 calls.
It is only possible to read this data (z) if the user has filtered the x and y columns and lenght(x) < 50.
Here is what I would like to do:
- If(lenght(x)<50) then load data from url
- url must be dynamic because it contains the variable x