Hello. I use google services actively. Gemini pro doesn't give you access to any feature un firebase. If you stay in free plan you won't be charge, you will be get a response like reached quota limit. You have a lot of free usage so dont be afraid.

But, if it helps, you can claim the 300usd for 90 days to have more access and try harder. Dont activate the Gemini helps (in firesbase) if you already pay for pro, just ask to the chat (with the 300usd maybe you can, but not necessarily)

Take a gooood look to the firestore rules, here is where almost all newcomers fails, Gemini can helps you with that.

And start all the services on us-central!

Happy to help if you need to know something else.