Under the NEC4 ECS form the Subcontractor is required to submit an application for payment which the Contractor considers when assessing the amount due. I can only assume that the Contractor has not made this assessment and certified payment within the required timescales, which is 2 weeks from the payment assessment date.
At s110B paragraph 4 of the amended ‘Construction Act’, where this situation occurs then the Subcontractor’s payment application would become the ‘default’ payment notice. This amount should be paid by the final date for payment, unless a valid notice of intention to pay less than the notified sum is given. You don’t need to give a further payment notice.
If a payment application has not been submitted the amount due is determined by sub-clause 50.4.