## 1 Introduction  
The resource-constrained project scheduling problem (RCPSP) is one of the most frequently undertaken issues within operational research. For RCPSP, optimizing models are often analyzed which only include time criteria, that is makespan minimization etc. [1]. In practice, however, an analysis of the financial effects of planned projects, in particular large-scale projects executed over a long period of time, plays an important role. For long-term projects it is recommended to take into account the change in the value of money over time, which occurs in Max-NPV (net present value maximization) models [2]. The optimization criterion of NPV maximization is the most common criterion that takes into account the financial aspects of project planning [3]. When calculating NPV, the sum of all discounted cash flows associated with the project is calculated. RCPSP models with discounted cash flows (RCPSP-DC) are considered. An overview of NPV maximization research can be found in the literature [4; 5]. Research works analyze payment project scheduling (PPS) models from the perspective of the contractor and/or the client. Payment schedules determine the frequency, amounts and delivery dates of client payments to the contractor. There are different methods for making financial settlements by compromise between the client and the contractor, whose interests in respect of the amount, timing and location of progress payments are divergent. The contractor aims to obtain the highest possible client payments as soon as possible. The client prefers to make a one-off payment after work. According to [PERSON] [6] both parties (client and contractor) are willing to maximize their profit instead of looking for a plan that satisfies them both. PPS problems are analyzed, where the solution from the perspective of client [7], the contractor [4; 8; 9] or both is sought [10; 11; 12; 13]. This work discusses the problem of financial optimization from the contractor's perspective. Contractor expenditures (cash outflows) are generally known or may be estimated by them prior to the project, while client payments are determined by negotiation. Different approaches are considered in which total costs for executing activities may be incurred at their beginning [6; 9] or completion [14], or may be proportionally allocated to the beginning and end of their execution [15; 16], or distributed depending on their progress [11]. Fixed costs related to the activities are most often incurred at the start time and other costs, such as resource consumption, may arise during their execution. As contractors are forced to spend money on project activities, it is advisable for them to acquire as much money as possible from the client prior to completing the project, such as, funds corresponding to the progress of the project. An improperly designed project settlement plan between the contractor and the client can cause financial problems for the contractor. Payments can be made in many ways [6; 9; 14; 17]. One-off lump-sum payments after completion of a lump sum payment (LSP) project are one of the forms of settlement between client and contractor, most preferred by the client. For long-term projects, the LSP model may be unacceptable to a contractor who has to spend a long time financing the activities. In practice, progress payments are often determined throughout the duration of the project. Earlier client payments are typically associated with certain events and with milestones (completion of specific activities, stages). In general, payments can be made according to a fixed schedule, such as once a month (Equal Time Intervals--ETI model, Progress Payments-PP model) or associated with specific events (Payments at Event Occurrences-PEO model), i.e., completion of activity (Payments at Activities' Completion times-PAC model) etc. [9; 17; 18]. PPS models serve as a decision support tool for negotiations between the client and the contractor and can be used when planning the contractor's budget.