What does BONA FIDES EXIGIT NT QUOD CONVENIT FIAT mean?

BONA FIDES EXIGIT NT QUOD CONVENIT FIAT meaning in Law Dictionary

Good faith demands that what is arranged will probably be done. Dig. 19, 20, 21; Id. 19, 1, 50; Id. 50, 8, 2, 13.