This may have been covered elsewhere, but what's the function of a here? I realise it's the same a that occurs with atá... is it just for question formation?
With cé and other question words there's an implied copula, thus you need the relative clause, marked with a.
A more literally translation of this is "Who is it that pays?"
ah interesting, thanks for this. Do you happen to know of a page that explains the analysis/questions in irish in more detail?
I suggest perusing this
Can you access (perusing this) from a nocia phone
Yes, that link works in the web browser on a Nokia phone.
It probably doesn't work in the Duolingo App on a phone, because Duolingo chose not to support links in the various different Duolingo mobile apps.