According to Malachi 3:8, how were the people robbing God?

Answer: In tithes and offerings

"Will a man rob God? Yet you are robbing Me!... In tithes and offerings."

“Will a man rob God? Yet you are robbing Me! But you ask, ‘How do we rob You?’ In tithes and offerings. You are cursed with a curse, yet you—the whole nation—are still robbing Me.”— Malachi 3:8-9 (BSB)