What should a Party do if he intends to withhold payment under Option Y(UK)2?

What should a Party do if he intends to withhold payment under Option Y(UK)2?

If either Party intends to withhold payment of an amount due, he notifies the other Party no later than seven days before the final date for payment. His notification should state the amount proposed to be withheld and the reason for withholding payment (see Clause Y2.3).