How to resolve conflicts with the customer's progress

This often occurs during project implementation:
The customer's demand is delayed, and the project launch date is approaching, so the project progress is facing huge online pressure. The customer requested more resources for this issue and went online as scheduled.

What should the project manager do in the face of such a situation?
If the project manager delays the launch on the grounds of insufficient resources, it will make the customer feel that we do not pay enough attention to this project, and lead to effective communication to stop and start a meaningless debate.
If you do the following, it will certainly have different results.
First, clarify the requirements as soon as possible and coordinate end users to participate in requirement confirmation.
Secondly, make a good project plan and WBS decomposition and confirm with the customer so that the customer can understand the problem and understand that the solution to the problem can be handled without adding resources.
Again, propose a phased release plan.

Finally, the issue is passed up to get coordination from higher-level leaders.