HTTP POST request to IFTTT
Problem I see is that the request is incomplete - the server will be waiting for your payload.

client.print(String("POST ") + url + " HTTP/1.1\r\n" +
           "Host: " + host + "\r\n" + 
           "Connection: close\r\n\r\n");


You haven't specified a Content-Length header so the payload should start after the headers finish - but you don't send anything.

You need to (at least):


add a payload or
add a Content-Length: 0 header or
add a payload with a matching Content-Length: header.


You can use curl to see a full set of valid POST headers like this:

curl -v -d "" http://localhost


You can use Chrome and Firefox's Web Inspector's Network tab to look at the raw headers of requests too.