There is the following deviation of Yucata's Antike Duellum implementation from the rules of the face-to-face game:
The game includes 14 coins. On p. IV of the rulebook, it says: "If the bank has no more coins, the player may choose whatever other type of resource he wishes instead."
The same is not true for resource chips (which do not include coins). On p. I of the rulebook, it says: "Only resource chips are unlimited. In the rare case the resource supply is not sufficient, you may use other counters such as pennies to indicate chips are now worth double their denomination."
The coin limit is not implemented in the Yucata version, there doesn't seem to be any limit on the number of coins allowed: I made a test game last month and the game allowed the sum of coins of both players to be larger than 20, at which point I aborted the test.
One *might* say that it is a limitation not necessary in the online game which doesn't have scarce coin chips, but it seems that although this situation shouldn't even occur in games too often, the game designer made a deliberate choice to include a limit for coins. In contrast to that, he declared resource chips as unlimited in spite of the game obviously only including a limited number. Maybe he wanted to avoid the possibility to amass large amounts of the flexible coins.
There is also a limit for both players' sum of cities for each of the resources (10 for gold, 12 for marble and 12 for iron) and for their sum of temples (12), which is implemented correctly on Yucata as far as I know.
So in the interest of staying true to the original version and its designer's intention, I'd say to treat this as a bug and implement a 14-coin-limit - at least if this is not too difficult.
So whenever the sum of coins of both players is 14, a player who would get a new coin should need to choose a resource instead.
Thanks in advance if this is possibe, ArkTheLad!