You can only play your game on multiple devices if you have linked to Runaway Login or Apple ID (iOS/Apple devices only).
To access your game on another device make sure to choose "log in" then:
For Runaway Login - enter your Runaway Login associated email and then either send an email confirmation link using the "email a sign in link" button or choose the "next" button to input your password if you have set one. If you have emailed a sign in link you will need to go to your email and open this and click the link before you will be logged in to Bird Kind
For Apple ID - choose the black "Sign in with Apple" button
When playing across more than one device always make sure that when finishing a play session on one device you wait at least 20 seconds between the last action and closing the game. When you close the game, please ensure it is fully force quit before opening your game on another device.