Your question is not at all stupid. I upvoted it.
The fedex documentation is horrible and doesn’t mention how to use their services while testing and after moving to production. Their support is worse.
While I was rambling in the internet, I found a page mentioning the tracking number 123456789012 as a test number. Use it with your test credentials (key, password, account number and meter number), while you’re setting your service path to https://wsbeta.fedex.com:443/web-services/track, and the request will return a valid response that you can build on.