Is per-customer project provisioning with distributed API keys allowed?

Gemini API
1

Hi,

I’m building a paid desktop app (Electron + local Python backend) for teachers in
Korea. It extracts questions from exam PDFs using the Gemini API. The PDF pages are
sent from the user’s own computer directly to the Gemini API — they never pass
through any server of mine.

Today each customer creates their own Gemini API key and pays Google directly.
I’d like to simplify this for non-technical users by covering the AI cost myself.
The design I’m considering:

  1. Create a separate Google Cloud project for each customer
  2. Link each project to MY billing account (so I pay, not the customer)
  3. Set a per-project spend cap to bound the cost
  4. Issue one API key per project and place it in that customer’s app installation
  5. When a customer’s subscription ends, unlink billing / delete that key

My questions:

(a) Is it permitted under the Gemini API Additional Terms of Service to issue API
keys from projects I own and place them in end users’ installed applications?
The API key best-practices docs advise against embedding keys in client apps,
but I couldn’t find an explicit prohibition in the Terms. Is this a security
recommendation, or a Terms violation?

(b) If it is not permitted, is there a supported way for a developer to pay for
end users’ Gemini API usage without proxying their content through the
developer’s servers?

(c) Are there limits I should know about on the number of projects that can be
linked to a single billing account for this pattern?

Thanks!