Settings on the Server

Select 'Connection' the Server permits when the Client tries to connect to the Server. There are three kinds of modes, 'Synchronous/Asynchronous', 'Synchronous', and 'Asynchronous'.
The default is 'Synchronous/Asynchronous'.

For example, if 'Synchronous' is selected on the Server, when the Client tries to connect to the Server in the 'Asynchronous' mode, the "Asynchronous connection failed" message appears and it doesn't connect.

Refer to the settings on the Client.
  → iPhone, iPad, iPod touch
  → Android