This app is currently in beta testing and is unavailable in the public app stores, however you can still install it as detailed below:
You can download the app using this link:
https://apps.apple.com/gb/app/gaskains/id6502653518
You can join the testing program using this link:
https://play.google.com/store/apps/details?id=uk.co.gaskains.app&pcampaignid=web_share