23 When he has filled his belly, God will vent his burning anger against him and rain down his blows on him.

Read Job 20:23 Using Other Translations

When he is about to fill his belly, God shall cast the fury of his wrath upon him, and shall rain it upon him while he is eating.
To fill his belly to the full, God will send his burning anger against him and rain it upon him into his body.
May God give them a bellyful of trouble. May God rain down his anger upon them.