diff --git a/chrome-extension/popup.js b/chrome-extension/popup.js
index 712b722..1ee352e 100644
--- a/chrome-extension/popup.js
+++ b/chrome-extension/popup.js
@@ -267,11 +267,15 @@ async function uploadHTTP(item, idx, prefix) {
     contentType: item.file.type || 'application/octet-stream'
   });
   if (!presigned.success) throw new Error(presigned.error);
+  // Use the content type from the server response (matches what was signed)
+  // NOT item.file.type which may differ from what the server determined
+  const signedContentType = presigned.contentType || item.file.type || 'application/octet-stream';
+  console.log(`[DW] Upload ${item.name} → ${presigned.url.substring(0, 60)}... (${signedContentType})`);
 
   await new Promise((resolve, reject) => {
     const xhr = new XMLHttpRequest();
     xhr.open('PUT', presigned.url);
-    xhr.setRequestHeader('Content-Type', item.file.type || 'application/octet-stream');
+    xhr.setRequestHeader('Content-Type', signedContentType);
     xhr.upload.onprogress = (e) => {
       if (e.lengthComputable) {
         const pct = Math.round((e.loaded / e.total) * 100);
@@ -279,8 +283,14 @@ async function uploadHTTP(item, idx, prefix) {
         setFileStatus(idx, 'uploading', `${pct}%`);
       }
     };
-    xhr.onload = () => xhr.status < 300 ? resolve() : reject(new Error(`S3 ${xhr.status}`));
-    xhr.onerror = () => reject(new Error('Network error'));
+    xhr.onload = () => {
+      console.log(`[DW] S3 PUT ${item.name} → ${xhr.status}`);
+      xhr.status < 300 ? resolve() : reject(new Error(`S3 error ${xhr.status}: ${xhr.responseText?.substring(0, 200)}`));
+    };
+    xhr.onerror = () => {
+      console.error(`[DW] S3 PUT ${item.name} network error`);
+      reject(new Error('Network error — check console for details'));
+    };
     xhr.send(item.file);
   });
   document.getElementById(`fpb-${idx}`).style.width = '100%';