PMP Practice: Survey all necessary parties to reach consensus

Cedar Tanaka is leading a hybrid project at Bright Pulse Labs to develop a customer-facing mobile app with both predictive infrastructure components and agile feature development. Three months into the project, the infrastructure team (working in two-month phases) delivered their first component to the agile feature teams (working in two-week sprints). The feature teams immediately escalated that the infrastructure API uses REST endpoints when they had built their entire sprint backlog assuming GraphQL. Both teams insist they communicated their technical approach in their respective planning sessions, which were held separately. The rework will delay the next three sprints and require infrastructure re-architecting. The project sponsor is demanding to know why this wasn't caught earlier. What should Cedar have done to prevent this misunderstanding?