I'm doing the career mission where I need to sell, aside from stone, 60 wine to Rome.
I have already sold 54, but now the mule train is just standing in front of the market building, which has 0 wine, even though I have several wineries in the city, all holding 5 wine.
Are the workers in the trade market not supposed to collect the goods to be traded? Or can they only pick them up from a granary?
If so, will I have to wait for the winemakers to decide it's time to deliver the wine to a granary?

I couldn't find a an answer for this either in-game or in the manual.

EDIT: I have just discovered that yes, it is like this.