For complex product flows, a so called 'wireflow' can help design and development teams to understand the system , before starting to create any highlevel prototype. This is a hybrid tool that combines sitemaps, flowcharts, and wireframes. The advantage of using a wireflow is that it's easy to convey the user's flow by maintaining a good level of fidelity, and keeping away from total abstraction.

It's however worth noting, that creating wireflows, same as wireframes should not be considered as design's first step. You need to first understand the journey that users take, questions that they ask, and the problems they face, and opportunities for improvement  that arise from those problems.

This can be done by mapping user journey for different scenarios