Design for touch and small screens
For a technical producer, this catalog design prototype should make every player action and result shown in the game easy to evaluate. Write how to define item identity, value, Koin price, preview, and ownership before checkout. Map preview, confirmation, a cancelled choice, a Koin shortage, pending, success, delivery, owned, and reload. Give every failure a safe next action. Use comfortably separated confirm and cancel controls, readable Koin amounts, and a layout that survives portrait, landscape, browser chrome, and an on-screen keyboard without hiding the item.
Expect interruption
Simulate locking the phone, changing tabs, receiving a call, and returning with a slow connection. The player should see one understandable result and retain a safe route back to play.
State the platform limit
A mobile browser prototype is not an App Store or Google Play binary. Native billing APIs, device identity, refunds, entitlements, and submission need separate implementation and review.
Name every state and owner
Separate preview, confirmation, pending, success, delivery, owned, insufficient Koin, cancel, interrupted, and reopened states. Assign later production work for identity, persistence, native billing, security, refunds, policy, and monitoring.
Define idempotent recovery
Repeated confirmation, a slow response, navigation during delivery, and reopening must resolve to one result. Record which state is authoritative and how the player can safely retry without another grant or Koin deduction.
Turn the prototype into tickets
Capture the visible behavior first, then create implementation tasks with expected examples for each transition and platform boundary. Do not translate a working browser interaction into an unsupported claim that backend commerce is complete.
Compare items consistently
Use the same fields for every offer: preview, benefit, ownership or duration, full price in Koin, and owned state. Consistent cards make differences easier to understand. Test that behavior using mobile web games. Mobile web is not the same as an App Store or Google Play binary.
Keep the first catalog small
Start with one to three clearly different items. A large grid makes it harder to find unclear value, duplicated promises, and missing delivery states. Test that behavior using mobile web games. Mobile web is not the same as an App Store or Google Play binary.
Design owned and unavailable states
A catalog also needs sold, owned, equipped, and unavailable presentations. Do not leave a purchased item looking buyable after reload. Test that behavior using mobile web games. Mobile web is not the same as an App Store or Google Play binary.