<p>Classic supply chain network design models usually assume that all demands are adequately fulfilled, although in practice most companies are selective in their target markets. By not fulfilling all demands, the unit profit margin is no longer constant as in the conventional cost-minimization network design models, because the size of demands is unknown. Additionally, current studies primarily focus on physical flows within the supply chain network, largely neglecting financial flows. However, payment delays are not uncommon in practice and can significantly affect various costs in supply chains. To address these issues, we propose a network design model with flexible demand fulfillment and delayed payments under capital constraints. It integrates the decisions of selective demand fulfillment, payment terms, safety stock levels, and multi-echelon inventory replenishment policies to maximize total profit. Efficient algorithms are developed by exploiting the structural properties of the model. In-depth analysis of the numerical study suggests that it is not always optimal to fulfill all demand sources. Moreover, accounting for payment delays leads to an optimal solution with more demand sources fulfilled, longer replenishment intervals, and eventually higher system wide profit. The impact of this financial arrangement further increases as the difference in the corresponding costs of capital between the firm and demand sources grows.</p>