Cannot insert duplicate key in object

I have a record type with following releation Request Master (one to one) Payment Request (One to One) Invoice Header (One to One) Invoice Payment Info but getting following error

Unable to write to or delete from the source due to a data integrity violation.
Error Details: Violation of UNIQUE KEY constraint 'UQ_PAYMENT_INFO_HEADER_INVOICE_ID'. Cannot insert duplicate key in object 'dbo.INVOICE_PAYMENT_INFO'. The duplicate key value is (21769).

Not sure why its throwing duplicate key as the ID PK attribute is blank