Payment channel networks (PCN) enable the use of cryptocurrencies in everyday life by solving the performance issues of blockchains. Nevertheless, the main implementations of payment channel networks lack the flexibility to test new proposals that can address fundamental challenges, such as efficient payment routing and maximization of the payment success rate. In this demo paper, we propose PCNsim, an open-source simulator based on OMNeT++, which fully reproduces the default behavior of a payment channel network. We build the simulator in a modular architecture that allows easy topology/workload customization and automates result visualization. The core mechanism of PCNsim implements the specifications of the Lightning Network. We evaluate our proposal with a dataset of credit card transactions in a scale-free topology and show that it successfully demonstrates the difference between two routing methods in different setups.