Question As a nominated subcontractor What step we can take if the client is not confirming the variation price after all the required and necessary substantiation.please note that this variation has already been approved by the engineer.
You did not mention the form of contract you are using. My reply will be general in nature.
If the Engineer already provided a fair determination after consulting both Parties, then it should be followed by both Parties.
You can obtain a decision over this dispute by referring the matter to DAB.