503 for specific client, need help

hey,
we have a AI product at our company and it requires clients to create a Gemini API key via google AI studio.

and we are all familiar with the 503 error (service unavailable) and that not our main issue,

we have many clients and our own keys running constantly hitting the API and it runs smooth, when we do hit 503 it effects all api request (as expected).

but we have one specific client that the past 2 weeks can’t use the key at all, this is a big issue.

we check every thing and it all looks fine but the key just keeps throwing 503 when all the other keys work fine

we even moved the client to Gemini API tier 2 by prepaying the minimum cost and still unavailable

we need help ASP, and i can provide more details

thanks alot