Gemini API returns 403 – “Your project has been denied access”

Hello,

My Gemini API project is enabled and the API key is active, but every
Gemini API generation request returns:

403 PERMISSION_DENIED:
Your project has been denied access. Please contact support.

Project name:
Default Gemini Project

Project ID:
gen-lang-client-01523024..

Project number:
506436828..

Billing tier:
Free tier

The Gemini API is enabled in Google Cloud Console.
The API key is active and restricted to the Gemini API.

Google AI Studio does not show a project restriction or denial message.
Google Cloud Console also does not show an appeal or request-review option.

However, an actual Gemini API inference request is rejected with the
project-denied 403.

Could you please check the access status of this project and explain why
Gemini API inference is being denied?

Thank you.