http request error - Request Error: error -

Hi All,

I keep getting the following error "Request Error: error - " when trying to run the following code:

let t := this;
let response := do as server
http("GET", t.URL)
end;
if response.error then
alert("Error " + text(response.error))
else
alert(text(response.result));
end

t.URL:

https://shipit-api.herokuapp.com/api/carriers/usps/<tracking_number>

Any help would be greatly appreciated.

Thanks,

Alex