Please update the Grasshopper apps for iOS and macOS to allow them to be set as the default calling and/or messaging app (app used to open tel: and sms: URLs).
In iOS, the default calling and messaging apps are configured in Settings > Apps > Default Apps but Grasshopper is not shown as an option.
In macOS, the default calling app is configured in FaceTime > Settings… > General > Default for calls, but Grasshopper is not shown as an option. There is not yet a location in macOS to set the default messaging app, but you can use third-party apps such as SwiftDefaultApps to configure which app is used to open sms: URLs.