code: public void enablePresence(String privateKey, String channel,
  			Boolean metadata, OnEnablePresence callback)
  			throws OrtcNotConnectedException {
  		if (!this.isConnected) {
  			throw new OrtcNotConnectedException();
  		} else {
  			String presenceUrl = this.isCluster ? this.clusterUrl : this.url;
  
  			Ortc.enablePresence(presenceUrl, this.isCluster,
  					this.applicationKey, privateKey, channel, metadata,
  					callback);
  		}
  	}
docs: Enables presence for the specified channel with first 100 unique metadata
  if metadata is set to true.
  
  <pre>
  Ortc.enablePresence(&quot;PRIVATE_KEY&quot;, &quot;CHANNEL&quot;, true, new onEnablePresence() {
  
  public void run(Exception error, String result) {
  if (error != null) {
  System.out.println(error.getMessage());
  } else {
  System.out.println(result);
  
  }
  }
  });
  </pre>
  
  @param privateKey
  The private key provided when the ORTC service is purchased.
  @param channel
  Channel with presence data active.
  @param metadata
  Defines if to collect first 100 unique metadata.
  @param callback
  Callback with error and result.
  @throws OrtcNotConnectedException