private void btn3Call1_Click(object sender, EventArgs e) { if (pbxCall1 != null) { // Release call rainbowTelephony.ReleaseCall(pbxCall1.Id, callback => { if (!callback.Result.Success) { String output = String.Format("Impossible to release call [{0}] - Error:[{1}]", pbxCall1.Id, Util.SerializeSdkError(callback.Result)); AddStateLine(output); log.LogError(output); } }); } }