What's the difference between "https://fapi.binance.com" and "https://testnet.binancefuture.com"

What’s the difference between “https://testnet.binancefuture.com/fapi/v1/order” and https://fapi.binance.com/fapi/v1/order ?

Order success!
https://testnet.binancefuture.com/fapi/v1/order?symbol=BTCUSDT&side=BUY&type=MARKET&quantity=0.1&timestamp=1641538915633&recvWindow=50100&signature=92a49e0ec07

Order failed
https://fapi.binance.com/fapi/v1/order?symbol=BTCUSDT&side=BUY&type=MARKET&quantity=0.1&timestamp=1641538812166&recvWindow=50100&signature=b50cc6948e1161

What’s the difference between the two orders?

https://testnet.binancefuture.com is a testing environment for you to try out the endpoints.
https://fapi.binance.com is a production environment where you trade with your assets.

You don’t have access.
400 error ???

What should I do?