COSS offers bundle purchases. A bundle is a way to purchase multiple apps/clockfaces in one transaction for a fraction of the total price.
Currently the Fitbit devices do not contain a unique user ID we developers can use. So if you purchase our Super Blowout Sale bundle you will be prompted for payment every time you switch clockface or re-install an app.
No worry, in such case just go to kzl.io/unlock, provide the email you used on the original purchase and your favourite clockface or app will be unlocked at no costs at all.
Soon this annoying issue will be solved by Fitbit.