Doing wrong to another person was the same as betraying the Lord:
Numbers 5:6-7 If any of the people—men or women—betray the Lord by doing wrong to another person, they are guilty. They must confess their sin and make full restitution for what they have done, adding an additional 20 per cent and returning it to the person who was wronged.
The penalty was similar to that of breaking a vow. It incurred a fine of an extra 20 per cent of the value of the offence (or broken vow).