How Can I Set a Spending Limit Per DeepSeek API Key?

Hello, Currently, I have 3 new interns at my small company. I want to introduce them to AI-assisted coding, so I'd like to give each of them a $10 monthly allowance to experiment with the DeepSeek API. What I did was create 3 separate API keys under my DeepSeek Platform account. However, they all share the same billing account and balance. While I can see the usage and costs for each API key, I haven't been able to figure out how to limit each key to a maximum spend of $10. Is there a way to do this? Thanks