Radical variant: ask the player to suggest consequences. I mean, the player understands and agrees that the PC violated the Oath, right?
Wait, the player doesn't? Then tell the player what exact words of the Oath they violated. Use your authority *at the table* before you use it *in the story*.
Wait, the player doesn't? Then tell the player what exact words of the Oath they violated. Use your authority *at the table* before you use it *in the story*.