diff --git a/backend/services/memberTransferService.js b/backend/services/memberTransferService.js
index 42b9400..f5e7207 100644
--- a/backend/services/memberTransferService.js
+++ b/backend/services/memberTransferService.js
@@ -165,6 +165,37 @@ class MemberTransferService {
                 }
             }
             
+            // Debug-Logging für Login-Credentials
+            if (loginEndpointUrl) {
+                if (loginCredentials && Object.keys(loginCredentials).length > 0) {
+                    devLog('[transferMembers] Login-Credentials gefunden:', Object.keys(loginCredentials));
+                    // Logge nur die Keys, nicht die Werte (Sicherheit)
+                    devLog('[transferMembers] Login-Endpoint:', loginEndpointUrl);
+                    devLog('[transferMembers] Login-Format:', config.loginFormat || 'json');
+                    
+                    // Mapping: Wenn "username" vorhanden ist, aber kein "email", verwende "username" als "email"
+                    // Viele APIs erwarten "email" statt "username"
+                    if (loginCredentials.username && !loginCredentials.email) {
+                        devLog('[transferMembers] Mappe "username" zu "email" für Login');
+                        loginCredentials.email = loginCredentials.username;
+                        // Entferne username, falls email erwartet wird
+                        // delete loginCredentials.username; // Auskommentiert, falls beide benötigt werden
+                    }
+                } else {
+                    devLog('[transferMembers] WARNUNG: Keine Login-Credentials gefunden!');
+                    devLog('[transferMembers] loginEndpointUrl:', loginEndpointUrl);
+                    devLog('[transferMembers] config.loginEndpoint:', config.loginEndpoint);
+                    devLog('[transferMembers] savedConfig vorhanden:', !!savedConfig);
+                    if (savedConfig) {
+                        const savedCreds = savedConfig.getLoginCredentials();
+                        devLog('[transferMembers] Gespeicherte Credentials vorhanden:', !!savedCreds && Object.keys(savedCreds).length > 0);
+                        if (savedCreds) {
+                            devLog('[transferMembers] Gespeicherte Credential-Keys:', Object.keys(savedCreds));
+                        }
+                    }
+                }
+            }
+            
             if (loginEndpointUrl && loginCredentials && Object.keys(loginCredentials).length > 0) {
                 try {
                     const loginResult = await this.performLogin(
@@ -411,6 +442,20 @@ class MemberTransferService {
      */
     async performLogin(endpoint, format, credentials) {
         try {
+            // Debug-Logging
+            devLog('[performLogin] Endpoint:', endpoint);
+            devLog('[performLogin] Format:', format);
+            devLog('[performLogin] Credential-Keys:', Object.keys(credentials || {}));
+            devLog('[performLogin] Credentials vorhanden:', !!(credentials && Object.keys(credentials).length > 0));
+            
+            if (!credentials || Object.keys(credentials).length === 0) {
+                return {
+                    success: false,
+                    error: 'Keine Login-Credentials übergeben',
+                    statusCode: 400
+                };
+            }
+            
             let requestConfig = {
                 url: endpoint,
                 method: 'POST',
@@ -425,6 +470,7 @@ class MemberTransferService {
                     'Content-Type': 'application/json'
                 };
                 requestConfig.data = credentials;
+                devLog('[performLogin] Sende JSON-Daten:', JSON.stringify(credentials, null, 2).replace(/("password"[^,}]*")([^"]*)(")/g, '$1***$3'));
             } else if (format === 'form-data' || format === 'multipart/form-data') {
                 const FormData = (await import('form-data')).default;
                 const formData = new FormData();