title: Google Calendar API: Calendar usage limits exceeded
body: <p>We have an application that does migrations between Google Apps domains.
  For calendar migrations we using Import API(<a href="https://developers.google.com/google-apps/calendar/v3/reference/events/import">https://developers.google.com/google-apps/calendar/v3/reference/events/import</a>). For last six months we did a lot of calendar migrations.
  But about week ago we faced with new API error for import:</p>
  
  <pre><code>    "error"=&gt;
    {"errors"=&gt;[
      {"domain"=&gt;"usageLimits",
      "reason"=&gt;"quotaExceeded",
      "message"=&gt;"Calendar usage limits exceeded."}], 
    "code"=&gt;403, 
    "message"=&gt;"Calendar usage limits exceeded."
  </code></pre>
  
  <p>Last week we got a lot of "Calendar usage limits exceeded." errors for users from different domains.
  Accordingly to Google API Console we didn't reach daily quota limit.
  For our app we using 2legged authorization.</p>
  
  <p>Please help us understand what does "Calendar usage limits exceeded." mean?
  How we can prevent this error?
  Where we can find information about Calendar usage limits?</p>