This error message from our iOS companion app will appear when your current version has become too far out of date. This message only comes up when it is absolutely necessary to upgrade your app version in order to continue using it with Hydrow.
Using the update button should get you into the process of updating to the latest version automatically. If it does not, you can also manually remove the Hydrow app from your device and download a fresh copy from the App Store.
Note that you may need to also upgrade to a compatible version of iOS in some cases to run the latest app. Right now devices running iOS 11 and earlier are not compatible with the Hydrow app.