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.