I've tested this, and I have no problems accessing the torproject.org API. Could you please try obtaining your server's IP, then accessing this URL manually: https://check.torproject.org/torbulkexitlist?ip=X.X.X.X&port=80
, and see if that works for you?
If you can access that URL in your browser, then your server's IP address has likely been blocked by the torproject.org server. You need to contact them for assistance if that is the case.