This app looks and works like a normal unit converter. To open your private chat, type your secret code as the amount, then tap the ⇅ swap button.
Remember your code: if you forget, delete and re-add the app (your messages stay online). You can turn the code on or off later in Settings.
The chat isn’t connected to its online storage yet. Once the setup is done, this screen goes away.
Use the email and password you signed up with.
Only two accounts can ever be created: yours and his.