According to best practices in project management, it is essential for the project manager to enforce the terms of the contract. If the updated schedule is a condition for milestone payment, the subcontractor is obligated to provide it, regardless of any verbal agreements with the client. The project manager should inform the subcontractor that in order to comply with the contract and process the payment, the updated schedule must be submitted. This ensures that all contractual obligations are met and that there is a clear record of the work completed, which is necessary for project tracking, reporting, and auditing purposes.

The answer is verified based on the principles found within the PMBOK® Guide and the standards of project management as outlined by the Project Management Institute (PMI). The PMBOK® Guide emphasizes the importance of contract management and the need for proper documentation and adherence to agreed-upon project schedules. Additionally, the Professional in Business Analysis (PMI-PBA) materials highlight the significance of maintaining accurate records and documentation for business analysis and project management activities.