Gemini API: Used over $3000 in July, but now getting constant 429 errors at $2000 in August

Issue encountered by a partner’s customer: Post-paid GCP, getting 429 errors when using the Gemini API

They used over $3,000 on the Gemini API in July, and have currently used a bit over $2,000 in August, but keep getting 429 errors.

According to the criteria for Tier 3, they already meet the requirements for Tier 3 (paid $1,000 + 30 days have passed since the first successful payment). Why are they still on Tier 2?

How should they proceed now?