"From here to there."
Is "פה" more common than "כאן" or is it just "מפה" that's more common than "מכאן"?
No difference at all. None. The sentence I wrote above is a line from a song, but the words are entirely interchangeable.
It would be really nice if there was some sort of usage guide for this one. According to morfix they mean the exact same thing. How are we supposed to know when to use which? It even has לבאן as a hint!
They are both fine. If Duolingo doesn't accept one or the other, report it.
In this case they're really the same. No differences in implications, formality, or any hidden profanities.