Basically what the title says. It worked if you select just one card of each type, but if you want to for example trash two silvers, I wasn't allowed to buy a card (it just trashed the cards) and skips to autoplay treasures option.
Thanks for the report, Bernaar!
As a general terminology remark, Forge doesn't allow you to buy a card, it allows you to gain a card. And the gained card needs to cost the exact amount of coins calculated from the trashed cards. So trashing 3 Silvers would mean you can gain a card costing exactly 9 coins, so it can be a Platinum, but not a Province.
I just tested this (with 3 Estates, and with your 2 Silvers) and I could gain a card each time.
What happened is probably one of 2 cases, the first being more likely if you just trashed 2 Silvers and nothing more, as you wrote:
1) There is exactly one card with the cost required by the conditions on Forge. In case of 2 Silvers trashed, that is a cost of 6 coins, which is what Gold costs and on many boards that's the only card that costs 6. In this case, as there is no actual choice to be made, the game will gain you the card automatically.
There should be an animation for a Gold going into your discard pile, but that can be missed or maybe you have animations disabled. In any case the gain should be in the game's log:
I plays a Forge.
I trashes 2 Silvers.
I gains a Gold.
2) There is no card with the cost required by the conditions on Forge. If you trash another Forge and 2 Silvers, you need to gain a card costing 13 coins. There is no card that costs that much, so you literally trashed 3 cards for nothing:
I plays a Forge.
I trashes 2 Silvers and a Forge.
You are right. I misunderstood the card. Works just fine like you say. Thanks! :)
No problem. Not needing to click on something that is "the only choice" is often a Boon, but can become a Hex when you not expect it. Have fun playing.