PSA5030 | Irregularities: Tax and NICs included in a calculation for items not covered by the PSA

From HM Revenue & Customs · PAYE Settlement Agreements

Where you discover that a calculation erroneously included tax and/or NICs on itemswhich were not covered by the terms of the agreement you must contact the employer to

obtain the full facts
establish why the amounts were included in the settlement and
explain that future calculations must be complete and correct

Depending on the details you obtain from the employer follow the guidance shown below

where there is a dispute over the items in a PSA see PSA5040
where eligible items have been included in the settlement but were not in the original agreement see PSA5050
where ineligible items have been included in the settlement see PSA5060