I had issues getting iOS deep links working, so I tried to start again from scratch by removing the cordova plugin and re-install it using the syntax below
Now when I try to build either Android or iOS I now get these errors
ionic-plugin-deeplinks is not set in the config.xml. The plugin plugin is not going to work.
No host is specified in the config.xml. Ionic Deeplinks Plugin is not going to work.
Although I still get the error, when I build and test the application out on my iPhone and Android phone the deep linking functionality actually works correctly. So I ignored the error and moved on. Hopefully it is the same for you!
Had the same issue and the reason was that in the config.xml the entries were defined with param instead of variable. So changed this and worked just fine. Have a look as this might be the case