title: Error while requesting a transaction with CXEndCallAction
body: <p>While requesting a CXTransaction with a CXEndCallAction, the transaction fails with error code 
  Error Domain=com.apple.CallKit.error.requesttransaction Code=4 "(null)"</p>
  
  <p>I was able to make a CXStartCallAction successfully. Does anyone know what this error means?</p>