Quick answer: Add per-account and per-IP rate limits to abuse-prone endpoints, make grants idempotent, and flag accounts whose request patterns are physically implausible.
Your reward-claim and score-submit endpoints have no rate limit, so a player scripts thousands of calls per minute to farm currency or spam the board. Add limits scoped to the account, not just the IP, and make repeated calls safe and detectable.
How to fix it
1. Rate-limit per account and IP
Apply limits keyed to the authenticated account in addition to IP, so rotating IPs does not bypass them. Return 429 and back off rather than processing the flood.
2. Make sensitive actions idempotent
Tie grants to a unique action ID so a burst of duplicate calls produces at most one reward, removing the incentive to spam.
3. Flag implausible patterns
Track per-account call rates and reward velocity, and queue accounts that claim rewards faster than gameplay allows for review rather than auto-granting.
Catching the ones you can't reproduce
The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.
Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.
This is where a tool like Bugnet earns its place. Its SDK captures every HTML5 error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.
Most of the time the fix is small. Seeing the failure clearly is the part that actually costs you.