Contracts are not a replacement for good communication between or within teams. In fact, contracts require collaboration and communication. One could make the argument that this is one of the main reasons to leverage Pact and enforce communication pathways in large internal and external development organizations.
Contracts are not a magical silver bullet that will allow you to hide in your developer caves and toss built artifacts at each other until everything passes. It is important for all teams to be invested in the process. One of the most common reasons that Pact fails to be successfully adopted in an organisation is a lack of buy in from all parties.
Collaborate about the problems, collaborate over the design, and keep the communication channels open.