Exam PMP topic 1 question 360 discussion

A project manager is assigned to a new marketing campaign. The sponsor gives the project manager an approved project management plan for review and explains the scope, business requirements, deliverables, and stakeholders. The project manager asks to see the project charter to gain a better understanding of the project. The sponsor says the project is small and simple so there is no need for a project charter.
What should the project manager do?