In the position below with white to move, 1.h5 fails
See Game 1927966
After the correct 1.Kd7, OTOH both players will be able to promote a pawn, but 3...a3 is a mistake for black. See Game 1929469
After the correct 3...axb3, white must play correctly to maintain the advantage. Game 1928000
offers an example of incorrect play.