Is regular payment to the contractor without being absolutely accurate … it should be a reasonable valuation of work completed (and materials, if they are to be paid before being fixed i.t.o. the agreement).

The principal agent can make adjustments in a subsequent payment certificate e.g. if work is subsequently condemned / broken down. The value of work completed will be reduced

See: 6.1P-25.2; 5.0P-31.1; 4.1P-31.1; 5.1M-19.2; 4.0M-13.3.2; 3.1M-13.3.2