Tier 1 billing enabled, but Gemini image model still returns free_tier quota limit 0 (429 RESOURCE_EXHAUSTED)

Hi team,

I’m using Gemini API from Google AI Studio and have already enabled billing (Tier 1).
However, image generation/editing requests are still rejected as Free Tier with limit 0.

Environment:

  • Region: Japan
  • API source: Google AI Studio API key
  • Model: gemini-3.1-flash-image-preview (error mentions gemini-3.1-flash-image)
  • Endpoint: models/*:generateContent
  • Billing: Enabled (Tier 1 shown in AI Studio)
  • I already regenerated API keys after enabling billing
  • I also configured budget alerts/limits, but issue persists

Error (HTTP 429):
RESOURCE_EXHAUSTED

What I already tried:

  1. Enabled billing and confirmed Tier 1 in AI Studio
  2. Regenerated API key in the billed project
  3. Waited for propagation and retried multiple times
  4. Verified project is linked to billing account

Could you please check if this project/key is stuck on Free Tier quota classification on backend?
I can share Project ID and request timestamps privately with moderators if needed.

Thank you.