If you used the PiAware image then the credentials are indeed pi and flightaware.
If you built your own software on top of a stock Raspbian build then the login will be pi and raspberry.
If neither of those work, check the caps lock key? Other than that, I once ran into a problem where I had a keyboard with the letter O that was broken. That threw me off for a couple days. Try tying the credentials into a text editor to make sure something weird isn’t happening