Question: What happens if you make an exposure with a misnamed tile.

Answer: If a player begins or completes their exposure with a misnamed tile their hand should be declared, “dead.” The player who incorrectly named the tile is not penalized however, if Mah Jongg is called with the incorrectly named tile, the game stops and the player who misnamed the tile pays the player who called Mah Jongg, 4 times the value of the hand.

Source: Mah Jongg Made Easy 2024, page 16, RULES AND PENALTIES, #3