diff --git a/web/src/reader/core/reader-navigation.ts b/web/src/reader/core/reader-navigation.ts
index 68fa25b..2ee08be 100644
--- a/web/src/reader/core/reader-navigation.ts
+++ b/web/src/reader/core/reader-navigation.ts
@@ -458,12 +458,35 @@ function sendProgressUpdate() {
   const state = getState();
   if (!state.currentReader || !state.readerMetadata) return;
 
+  const mediaItemId =
+    state.readerMetadata.media_item_id ||
+    document.body.dataset.mediaItemId ||
+    window.location.pathname.split("/").pop();
+
+  if (!mediaItemId) {
+    console.warn("No mediaItemId available for progress update");
+    return;
+  }
+
   let currentPage = 0;
   let totalPages = 0;
 
   if (state.currentReader.type === "ebook") {
-    currentPage = state.currentReader.currentSpineIndex + 1;
-    totalPages = state.currentReader.cif.spine.length;
+    // Use dynamic page calculation if available
+    if (pageCalculationResult) {
+      const container = document.getElementById("reader-content");
+      const viewportHeight = window.innerHeight;
+      currentPage = getCurrentPageFromScroll(
+        pageCalculationResult,
+        state.currentReader.currentSpineIndex,
+        container?.scrollTop || 0,
+        viewportHeight,
+      );
+      totalPages = pageCalculationResult.totalPages;
+    } else {
+      currentPage = state.currentReader.currentSpineIndex + 1;
+      totalPages = state.currentReader.cif.spine.length;
+    }
   } else if (state.currentReader.type === "pdf") {
     totalPages = state.readerMetadata.total_pages || 0;
     currentPage = state.currentReader.currentPage;
diff --git a/web/src/reader/core/reader-services.ts b/web/src/reader/core/reader-services.ts
index 30c3a12..31e146a 100644
--- a/web/src/reader/core/reader-services.ts
+++ b/web/src/reader/core/reader-services.ts
@@ -9,11 +9,19 @@ export async function updateReadingProgress(
   mediaItemId: string,
   progress: ReadingProgress,
 ): Promise<void> {
+  if (!mediaItemId || mediaItemId === "undefined") {
+    console.warn("Skipping progress update - no valid mediaItemId");
+    return;
+  }
   const response = await apiPut(
     `/media-items/${mediaItemId}/progress`,
     progress,
   );
-  await response.json();
+  if (!response.ok) {
+    const errorText = await response.text();
+    console.warn("Progress update failed:", response.status, errorText);
+    return;
+  }
 }
 
 export function getChapterNavigation(chapters: any[]) {