Dear Kollel
The Gemora says that the statement of Rav Ashi is not accepted, and learns from the Pasuk of Atem Gam Atem that just as the Goy cannot be the Sheliach of the Jew when it involves separating Trumah , so too he cannot be the Sheliach of the Jew when advancing the Jews money to someone else, ... that in both cases the Goy cannot be a Sheliach for the Jew.
But the Gemora does not differentiate between Trumah and monetary cases. --- by Trumah it is not just an action that is taking place but a Chalos, in that Tevel becomes Trumah There is a change in the Halachic status of the produce. Similarly a Chalos takes place by Kidushin and Gerushin, so in such cases a Goy cannot be a Sheliach for a Jew --- but by advancing money on behalf of a Jew there is no Chalos taking place, it is merely an action without a change in status.
Thank You
Nosson Tzvi
"Zechiyah" of money is also a chalos. A can give money to B in order that B should be "mezakeh" the money to C, and the money belongs to C even though it is physically still in the hands of B. This is what happened in our Gemara so Zechiyah is just as much of a chalos as Terumah.
Chanukah Sameach
Dovid Bloom