Background: Poor communication of requirements between clients and suppliers contributes to project overruns,in both software and infrastructure projects. Existing literature offers limited insights into the communication challenges at this interface. Aim: Our research aim to explore the processes and associated challenges with requirements activities that include client-supplier interaction and communication. Method: we study requirements validation, communication, and digital asset verification processes through two case studies in the road and railway sectors, involving interviews with ten experts across three companies. Results: We identify 13 challenges, along with their causes and consequences, and suggest solution areas from existing literature. Conclusion: Interestingly, the challenges in infrastructure projects mirror those found in software engineering, highlighting a need for further research to validate potential solutions.