diff --git a/go_cloud/internal/http/wopi_handlers.go b/go_cloud/internal/http/wopi_handlers.go
index 930cd58..92ad87c 100644
--- a/go_cloud/internal/http/wopi_handlers.go
+++ b/go_cloud/internal/http/wopi_handlers.go
@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"net/url"
 	"strings"
 	"sync"
 	"time"
@@ -664,14 +663,13 @@ func collaboraProxyHandler(w http.ResponseWriter, r *http.Request, db *database.
 	// Build WOPISrc URL
 	wopiSrc := fmt.Sprintf("https://go.b0esche.cloud/wopi/files/%s?access_token=%s", fileID, accessToken)
 
-	// Build Collabora editor URL with WOPISrc in query string
-	collaboraEditorURL := fmt.Sprintf("%s/loleaflet/dist/loleaflet.html?WOPISrc=%s", collaboraURL, url.QueryEscape(wopiSrc))
-
 	// Return HTML page with auto-submitting form
+	// Collabora requires: POST to /loleaflet/dist/loleaflet.html with WOPISrc in request body
 	htmlContent := fmt.Sprintf(`<!DOCTYPE html>
 <html>
 <head>
   <title>Loading Document...</title>
+  <meta charset="utf-8">
   <style>
     body { margin: 0; padding: 0; background: #f5f5f5; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; }
     .container { display: flex; justify-content: center; align-items: center; height: 100vh; }
@@ -682,15 +680,24 @@ func collaboraProxyHandler(w http.ResponseWriter, r *http.Request, db *database.
   <div class="container">
     <div class="message">Loading document in Collabora Online...</div>
   </div>
-  <iframe id="collabora-frame" style="display:none; width:100%%; height:100%%; border:none;"></iframe>
+  <form method="POST" action="%s/loleaflet/dist/loleaflet.html" target="collabora-frame" id="collaboraForm" style="display: none;">
+    <input type="hidden" name="WOPISrc" value="%s">
+  </form>
+  <iframe name="collabora-frame" id="collabora-frame" style="width:100%%; height:100%%; border:none; position:absolute; top:0; left:0;"></iframe>
   <script>
-    // Load Collabora editor in iframe
-    var frame = document.getElementById('collabora-frame');
-    frame.style.display = 'block';
-    frame.src = '%s';
+    (function() {
+      var form = document.getElementById('collaboraForm');
+      var frame = document.getElementById('collabora-frame');
+      if (form && frame) {
+        console.log('[COLLABORA] Submitting form to Collabora...');
+        form.submit();
+      } else {
+        console.error('[COLLABORA] Form or frame element not found!');
+      }
+    })();
   </script>
 </body>
-</html>`, collaboraEditorURL)
+</html>`, collaboraURL, wopiSrc)
 
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	// Don't set X-Frame-Options - this endpoint is meant to be loaded in an iframe
