How does the game decide where you can and can't place cards? I've had it force me to play on a diagonal rather than fill out a horizontal path with the same amount of cards
If you check the 'I' button on the top left it explains how you need to place cards. If you cannot form a valid hand, you cannot play In that direction. If you could do a valid hand and it didn't let you play, maybe it was a bug :(
