Unpaid Advanced Payment Code Notice

We are in the process of selling our (freehold) house, on a Persimmon estate. Our house is situated on an unadopted road, and our buyer’s solicitor has informed ours that an unpaid Advanced Payment Code is still active for our property. Further research suggests Persimmon should have paid this before commencing the build, but didn’t.

Does anyone know anything about these, and whether our buyer’s would be liable to pay this? Can we be indemnified against this, if so?