Question: What happens if during the Charleston a player discovers they do not have enough tiles?

Answer: If during the Charleston a player discovers they do not have enough tiles, everyone throws in their tiles, rebuilds their wall and the tiles dealt again. The only exception to this rule is, if the player to the left of East forgot to take their 13th tile, they may do so.

Source: Mah Jongg Made Easy 2024, page 14, bullet #1