diff --git a/src/app/portfolio/[slug]/remote-assessment/useCreateRemoteAssessment.tsx b/src/app/portfolio/[slug]/remote-assessment/useCreateRemoteAssessment.tsx
index 2db416d..8aa29ce 100644
--- a/src/app/portfolio/[slug]/remote-assessment/useCreateRemoteAssessment.tsx
+++ b/src/app/portfolio/[slug]/remote-assessment/useCreateRemoteAssessment.tsx
@@ -123,47 +123,35 @@ function useCreateRemoteAssessment({
 
   const { assetListFileKey, valuationDataFileKey } = useMemo(
     () => generateS3Keys(userId, portfolioId),
-    [userId, portfolioId]
+    [userId, portfolioId],
   );
 
-  const uploadMutation = useMutation({
-    mutationFn: uploadCsvToS3,
-  });
+  const uploadFileMutation = useMutation({
+    mutationFn: async ({
+      userId,
+      portfolioId,
+      fileKey,
+      csvFile,
+    }: {
+      userId: string;
+      portfolioId: string;
+      fileKey: string;
+      csvFile: Blob;
+    }) => {
+      // 1) Get presigned URL
+      const { url } = await generatePresignedUrl({
+        userId,
+        portfolioId,
+        fileKey,
+      });
 
-  const presignedMutation = useMutation({
-    mutationFn: generatePresignedUrl,
-    onSuccess: (data) => {
-      let csvFile: Blob;
-      if (data.fileKey === assetListFileKey) {
-        const assetList: {
-          uprn: number | null | undefined;
-          address: string;
-          postcode: string;
-          property_type?: string;
-          built_form?: string;
-        }[] = [
-          {
-            uprn,
-            address: addressLineOne,
-            postcode,
-          },
-        ];
+      // 2) Upload to S3
+      await uploadCsvToS3({
+        presignedUrl: url,
+        file: csvFile,
+      });
 
-        // if we have property type and built form, include them. Handle typescript optionality
-        if (propertyType) {
-          assetList[0]["property_type"] = propertyType;
-        }
-        if (builtForm) {
-          assetList[0]["built_form"] = builtForm;
-        }
-
-        csvFile = new Blob([convertToCSV(assetList)], { type: "text/csv" });
-      } else {
-        const valuationData = [{ uprn, valuation }];
-        csvFile = new Blob([convertToCSV(valuationData)], { type: "text/csv" });
-      }
-
-      uploadMutation.mutate({ file: csvFile, presignedUrl: data.url });
+      return true;
     },
   });
 
@@ -196,27 +184,51 @@ function useCreateRemoteAssessment({
   }
 
   async function handleSubmit(formData: RemoteAssessmentFormValues) {
+    // Build asset CSV
+    const assetList = [
+      {
+        uprn,
+        address: addressLineOne,
+        postcode,
+        ...(propertyType && { property_type: propertyType }),
+        ...(builtForm && { built_form: builtForm }),
+      },
+    ];
+
+    const assetCsv = new Blob([convertToCSV(assetList)], {
+      type: "text/csv",
+    });
+
+    // Build valuation CSV
+    const valuationCsv = new Blob([convertToCSV([{ uprn, valuation }])], {
+      type: "text/csv",
+    });
+
+    // Upload asset list and valuation data and wait
     await Promise.all([
-      presignedMutation.mutateAsync({
+      uploadFileMutation.mutateAsync({
         userId,
         portfolioId,
         fileKey: assetListFileKey,
+        csvFile: assetCsv,
       }),
-      presignedMutation.mutateAsync({
+      uploadFileMutation.mutateAsync({
         userId,
         portfolioId,
         fileKey: valuationDataFileKey,
+        csvFile: valuationCsv,
       }),
     ]);
 
+    // Now trigger engine (files guaranteed in S3)
     await triggerEngine(formData);
   }
 
   return {
     handleSubmit,
     triggerEngine,
-    isUploading: uploadMutation.isLoading || presignedMutation.isLoading,
-    hasError: uploadMutation.isError || presignedMutation.isError,
+    isUploading: uploadFileMutation.isPending,
+    hasError: uploadFileMutation.isError,
   };
 }