2381. The life annuity is due to the annuitant only in proportion to the number of days in the lifetime of the person upon whose life the duration of payment of the annuity was established, and the annuitant may not require payment of the annuity unless he establishes the existence of the person.
Where it was stipulated that the annuity would be paid in advance, however, every amount that should have been paid is acquired from the day payment was to have been made.