diff --git a/transfer/transfer-01-file-transfer/status-checker/src/main/java/org/eclipse/edc/sample/extension/checker/SampleFileStatusChecker.java b/transfer/transfer-01-file-transfer/status-checker/src/main/java/org/eclipse/edc/sample/extension/checker/SampleFileStatusChecker.java
index f64e8581..9eb5268a 100644
--- a/transfer/transfer-01-file-transfer/status-checker/src/main/java/org/eclipse/edc/sample/extension/checker/SampleFileStatusChecker.java
+++ b/transfer/transfer-01-file-transfer/status-checker/src/main/java/org/eclipse/edc/sample/extension/checker/SampleFileStatusChecker.java
@@ -27,7 +27,7 @@ public class SampleFileStatusChecker implements StatusChecker {
     @Override
     public boolean isComplete(TransferProcess transferProcess, List<ProvisionedResource> resources) {
         var destination = transferProcess.getDataRequest().getDataDestination();
-        var path = destination.getProperty("path");
+        var path = destination.getStringProperty("path");
         return Optional.ofNullable(path)
                 .map(this::checkPath)
                 .orElse(false);
diff --git a/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSinkFactory.java b/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSinkFactory.java
index 93b0472f..e7befc2a 100644
--- a/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSinkFactory.java
+++ b/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSinkFactory.java
@@ -40,17 +40,12 @@ public boolean canHandle(DataFlowRequest request) {
         return "file".equalsIgnoreCase(request.getDestinationDataAddress().getType());
     }
 
-    @Override
-    public @NotNull Result<Boolean> validate(DataFlowRequest request) {
-        return Result.success(true);
-    }
-
     @Override
     public DataSink createSink(DataFlowRequest request) {
         var destination = request.getDestinationDataAddress();
 
         // verify destination path
-        var path = destination.getProperty("path");
+        var path = destination.getStringProperty("path");
         // As this is a controlled test input below is to avoid path-injection warning by CodeQL
         var destinationFile = new File(path.replaceAll("\\.", ".").replaceAll("/", "/"));
 
@@ -62,4 +57,9 @@ public DataSink createSink(DataFlowRequest request) {
                 .monitor(monitor)
                 .build();
     }
+
+    @Override
+    public @NotNull Result<Void> validateRequest(DataFlowRequest request) {
+        return Result.success();
+    }
 }
diff --git a/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSourceFactory.java b/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSourceFactory.java
index 459cce6d..3712b9ce 100644
--- a/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSourceFactory.java
+++ b/transfer/transfer-01-file-transfer/transfer-file-local/src/main/java/org/eclipse/edc/sample/extension/api/FileTransferDataSourceFactory.java
@@ -29,27 +29,27 @@ public boolean canHandle(DataFlowRequest dataRequest) {
     }
 
     @Override
-    public @NotNull Result<Boolean> validate(DataFlowRequest request) {
+    public DataSource createSource(DataFlowRequest request) {
         var source = getFile(request);
-        if (!source.exists()) {
-            return Result.failure("Source file " + source.getName() + " does not exist!");
-        }
-
-        return Result.success(true);
+        return new FileTransferDataSource(source);
     }
 
     @Override
-    public DataSource createSource(DataFlowRequest request) {
+    public @NotNull Result<Void> validateRequest(DataFlowRequest request) {
         var source = getFile(request);
-        return new FileTransferDataSource(source);
+        if (!source.exists()) {
+            return Result.failure("Source file " + source.getName() + " does not exist!");
+        }
+
+        return Result.success();
     }
 
     @NotNull
     private File getFile(DataFlowRequest request) {
         var dataAddress = request.getSourceDataAddress();
         // verify source path
-        var sourceFileName = dataAddress.getProperty("filename");
-        var path = dataAddress.getProperty("path");
+        var sourceFileName = dataAddress.getStringProperty("filename");
+        var path = dataAddress.getStringProperty("path");
         // As this is a controlled test input below is to avoid path-injection warning by CodeQL
         sourceFileName = sourceFileName.replaceAll("\\.", ".").replaceAll("/", "/");
         path = path.replaceAll("\\.", ".").replaceAll("/", "/");
diff --git a/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/MarkerFileCreator.java b/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/MarkerFileCreator.java
index 4caafabe..4f2714f4 100644
--- a/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/MarkerFileCreator.java
+++ b/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/MarkerFileCreator.java
@@ -39,7 +39,7 @@ public MarkerFileCreator(Monitor monitor) {
      */
     @Override
     public void preCompleted(final TransferProcess process) {
-        Path path = Path.of(process.getDataRequest().getDataDestination().getProperty("path"));
+        Path path = Path.of(process.getDataRequest().getDataDestination().getStringProperty("path"));
         if (!Files.isDirectory(path)) {
             path = path.getParent();
         }
diff --git a/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/TransferListenerExtension.java b/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/TransferListenerExtension.java
index bed49254..6534e2d0 100644
--- a/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/TransferListenerExtension.java
+++ b/transfer/transfer-02-file-transfer-listener/listener/src/main/java/org/eclipse/edc/sample/extension/listener/TransferListenerExtension.java
@@ -43,7 +43,7 @@ public void initialize(ServiceExtensionContext context) {
     private static class FileStatusChecker implements StatusChecker {
         @Override
         public boolean isComplete(TransferProcess transferProcess, List<ProvisionedResource> resources) {
-            var path = transferProcess.getDataDestination().getProperty("path");
+            var path = transferProcess.getDataDestination().getStringProperty("path");
             return path != null && new File(path).exists();
         }
     }