EN
A mathematical model of the process of payment for purchases in an online store has been pre-sented. The model belongs to the class of semi-open queueing networks with four phases of exponential servers and Poisson arrivals. The authors describe in detail the derivation of the equations describing the system. Analytic expressions are derived on the basis of the proposed model for the average number of online store customers who have already paid for goods. Practical implementation of the model allows us to determine the number of clients who have added goods to their cart, but have not yet passed through the payment verification system, and thus determine the stream of real customers of the online store.