La. Civ. Code art. 1866
Current with changes from the 2024 legislative session, Chs. 3, 6-496, effective on or before 7/1/2024
An obligor of a debt that bears interest may not, without the obligee's consent, impute a payment to principal when interest is due.
A payment made on principal and interest must be imputed first to interest.
La. C.C. § 1866