Ralvo is a NPC in Divinity: Original Sin 2.
If you mess up and forget to play the sparkler card, just say you don't have any money and talk to him again for another round of cards.
100 gold i got there (on the hard difficulty, don't know if there are any differences)
I found a card called 'The Sparkler' on the drunken man Doctor Leste is attending to after he died. You can play that card and win some gold (not sure how much as it didn't say). You may have to play the first round with him and either pay up or talk your way out of it before the drunken man dies and is lootable.