As a Project Manager you are a 'specified person' under the 'Construction Act' and are required to give a notice (payment certificate) stating the amount considered due (to be paid) and the basis upon which that assessed amount is calculated.
Provided you have complied with the above then the payment certificate is the 'payment notice' under the 'Construction Act' and is the amount to be paid by the Employer / Client by the final date for payment.
A notice to pay less than the notified sum ('payless notice') is only relevant where the payer (Employer / Client) intends to pay a lesser amount than what is certified on the payment certificate.
Provided you have complied with the above then the payment certificate is the 'payment notice' under the 'Construction Act' and is the amount to be paid by the Employer / Client by the final date for payment.
A notice to pay less than the notified sum ('payless notice') is only relevant where the payer (Employer / Client) intends to pay a lesser amount than what is certified on the payment certificate.