Having DirecTV Whole Home service allows your receivers to communicate with each other, primarily for the purpose of watching content from one DVR on another receiver or DVR. However, just because the receivers can communicate with each other does not necessarily mean that they can communicate with anything else outside of the "Whole Home" network. In order for that to happen, you also need what is called the Cinema Connection Kit or CCK for short.
The CCK connects your DirecTV Whole Home network to your home network. This then allows you to watch DirecTV On Demand content as well as listen to Pandora Internet radio and watch YouTube videos right on your TV. It also allows you to control any receiver or DVR in your house through your home network, which is how the DirecTV Remote app works!
If you are not sure whether or not you have the CCK or simply cannot seem to control your DirecTV receivers then I'd suggest following the steps for confirming your DirecTV receiver/DVR settings found right here on this site. If the IP addresses found in the receivers do not "match" the IP address reported in the app then there is a good chance you do not have the CCK. This would also be indicated by the receiver/DVR reporting that it is not connected to the Internet.
If you definitely do have the CCK installed then another possible reason for not being able to control your receiver(s) through the app is if you do not have your Whole Home options set correctly in the receiver or DVR itself. The steps outlined in the FAQ linked above will also walk you through that as well.
For more information on the CCK, please see DirecTV's website. They also have installation instructions which tell you how to connect it to your home network should you decide to self-install it. The CCK can be purchased from them or at other online stores that sell DirecTV parts and equipment. You may also choose to have DirecTV install it for you.