How to enable In-Person signing in .NET (Sandbox user)

            // build the package defining the signers and document
            var oViolationPackage =
            PackageBuilder.NewPackageNamed(_sPackageName)
                .DescribedAs(_sPackageDescription)
                .WithSettings(DocumentPackageSettingsBuilder.NewDocumentPackageSettings().WithInPerson())
                .WithSenderInfo(oSenderInfo)
                .WithSigner(employeeSigner)
                .WithSigner(supervisorSigner)
                .WithDocument(
                    DocumentBuilder.NewDocumentNamed(Path.GetFileName(pathFileName))
                        .FromStream(fs, DocumentType.PDF)
                        .WithSignature(
                            employeeSignature
                                .WithPositionAnchor( TextAnchorBuilder.NewTextAnchor(signer1st.Ident())
                                .WithOccurrence( 9 )
                                .AtPosition(TextAnchorPosition.TOPLEFT)
                                .WithOffset(nSignatureOffSetLeft, nSignatureOffsetTop)
                                .WithSize(nSignatureWidth, nSignatureHeight)
                                )
                            )
                        .WithSignature(
                            supervisorSignature
                                .WithPositionAnchor( TextAnchorBuilder.NewTextAnchor(signer2nd.Ident())
                                .WithOccurrence(9)
                                .AtPosition(TextAnchorPosition.TOPLEFT)
                                .WithOffset(nSignatureOffSetLeft, nSignatureOffsetTop)
                                .WithSize(nSignatureWidth, nSignatureHeight)
                                )
                            )
                        )
                .Build();

            // add third signature
            if (signerOptional != null)
            {
                TextAnchor ta = TextAnchorBuilder.NewTextAnchor(signerOptional.Ident())
                    .AtPosition(TextAnchorPosition.TOPLEFT)
                    .WithOffset(nSignatureOffSetLeft, nSignatureOffsetTop)
                    .WithSize(nSignatureWidth, nSignatureHeight)
                    .Build();
                Signature signature = thirdSignature.WithPositionAnchor(ta).Build();

                oViolationPackage.Documents[0].Signatures.Add(signature);
            }

            if (_bSigningOrder)
            {   // signers are notified in order
                oViolationPackage.GetSigner(signer1st.Email()).SigningOrder = 1;
                oViolationPackage.GetSigner(signer2nd.Email()).SigningOrder = 2;
                if (signerOptional != null)
                {
                    oViolationPackage.GetSigner(signerOptional.Email()).SigningOrder = 3;
                }
            }
            if (_bSigningParty)
            {
                oViolationPackage.Settings.EnableInPerson = true;
            }