diff --git a/go_cloud/internal/http/wopi_handlers.go b/go_cloud/internal/http/wopi_handlers.go
index d98a865..941db42 100644
--- a/go_cloud/internal/http/wopi_handlers.go
+++ b/go_cloud/internal/http/wopi_handlers.go
@@ -5,7 +5,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"net/url"
+
+	//"net/url"
 	"strings"
 	"sync"
 	"time"
@@ -664,11 +665,8 @@ 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
-	// Collabora expects: /cool/dist/cool.html?WOPISrc=...
-	editorURL := fmt.Sprintf("%s/cool/dist/cool.html?WOPISrc=%s&closebutton=1", collaboraURL, url.QueryEscape(wopiSrc))
-
-	// Return HTML page that loads Collabora in an iframe
+	// Return HTML page with auto-submitting form
+	// Collabora Online requires: POST to /cool/dist/cool.html with WOPISrc in request body
 	htmlContent := fmt.Sprintf(`<!DOCTYPE html>
 <html>
 <head>
@@ -677,39 +675,33 @@ func collaboraProxyHandler(w http.ResponseWriter, r *http.Request, db *database.
   <style>
     * { margin: 0; padding: 0; box-sizing: border-box; }
     html, body { width: 100%%; height: 100%%; overflow: hidden; }
-    #collabora-container { width: 100%%; height: 100%%; background: #f5f5f5; }
-    #collabora-frame { width: 100%%; height: 100%%; border: none; }
-    .loading { position: absolute; top: 50%%; left: 50%%; transform: translate(-50%%, -50%%); text-align: center; }
-    .loading p { color: #666; margin-top: 10px; }
+    .loading { position: fixed; top: 50%%; left: 50%%; transform: translate(-50%%, -50%%); text-align: center; background: white; padding: 20px; border-radius: 8px; box-shadow: 0 2px 8px rgba(0,0,0,0.1); }
+    .loading p { color: #666; margin-top: 10px; font-family: system-ui, sans-serif; }
   </style>
 </head>
 <body>
-  <div id="collabora-container">
-    <div class="loading">
-      <p>Loading Collabora Online...</p>
-    </div>
-    <iframe id="collabora-frame"></iframe>
+  <div class="loading">
+    <p>Loading Collabora Online...</p>
   </div>
+  <form method="POST" action="%s/cool/dist/cool.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="position:fixed; top:0; left:0; width:100%%; height:100%%; border:none;"></iframe>
   <script>
     window.addEventListener('load', function() {
-      var frame = document.getElementById('collabora-frame');
-      var loading = document.querySelector('.loading');
-      
-      if (frame) {
-        frame.onload = function() {
-          if (loading) loading.style.display = 'none';
-        };
-        frame.onerror = function() {
-          console.error('[COLLABORA] Frame load error');
-        };
-        
-        console.log('[COLLABORA] Loading editor from:', '%s');
-        frame.src = '%s';
-      }
+      setTimeout(function() {
+        var form = document.getElementById('collaboraForm');
+        if (form) {
+          console.log('[COLLABORA] Submitting form to /cool/dist/cool.html');
+          form.submit();
+        } else {
+          console.error('[COLLABORA] Form not found');
+        }
+      }, 100);
     });
   </script>
 </body>
-</html>`, editorURL, editorURL)
+</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
