Is the difference in the value of a study course for the same duration (6 months) due to the difference in payment method (two installments or one payment) considered a form of usury (riba)?

The difference in the amount paid for the same duration due to deferment is neither usury (riba) nor problematic, as long as the agreement at the time of registration is specifically for one of the two transactions. So, if one of the two prices is specified before parting ways, the sale is permissible. However, if they part ways with ambiguity, it is not permissible.