The source for this is the Suda, which is an encyclopedic work upon which criticism is sometimes heaped. I include it for its trivia sake.
"The danikon is in currency at Great Antioch of Syria, which they use for small transactions".
ἐπιχωριάζει τῇ μεγάλῃ Ἀντιοχείᾳ τῆς Συρίας τὸ δανικόν, ᾧπερ χρῶνται εἰς μικρὰς πραγματείας.
"This is the name of a coin which in the old days they gave to the corpses as they buried them, as the fare on the boat over Acherousia. Acherousia is a lake in Hades, which the dead cross, and as they do so they give the aforementioned coin to the ferryman".
Δανάκη: τοῦτο νομίσματός ἐστιν ὄνομα, ὃ τοῖς νεκροῖς ἐδίδοσαν πάλαι συγκηδεύοντες: νεὼς Ἀχερουσίας ἐπίβαθρον. Ἀχερουσία δέ ἐστι λίμνη ἐν ᾅδου, ἣν διαπορθμεύονται οἱ τελευτῶντες τὸ προειρημένον νόμισμα τῷ πορθμεῖ διδόντες.