title: Why is LinkedIn API returning "999: request failed" message?
body: <p>I have been using the LinkedIn API without trouble for a while and suddenly today calls that used to work started failing. The API returns an HTML page titled "999: request failed". The body of the page says "Sorry, we are unable to serve your request at this time due to unusual traffic from your network connection."</p>
  
  <p>What does LinkedIn mean by "unusual activity"?</p>
  
  <p>Has LinkedIn implemented limits to the number of calls my application can make in a day? If so, what are they?</p>
  
  <p>Or, are they stopping calls from the IP address of my application's VPC? Is there a way to determine the reason?</p>