NIM15215 | Class 1A National Insurance contributions: Calculating Class 1A NICs: Amounts made good by the employee: Making good payments reduce earnings chargeable to income tax: Employer requests refund of Class 1A NICs paid

From HM Revenue & Customs · National Insurance Manual

NIM15211 explains the effect making good has on Class 1A NICs liability.

If an employer pays Class 1A NICs and later requests a refund of Class 1A NICs on amounts made good which were paid after the Class 1A NICs were due, no refund of Class 1A NICs is due, see NIM17130.