diff --git a/Classes/Domain/Repository/LogRepository.php b/Classes/Domain/Repository/LogRepository.php
index f9c9bbc..0f1b542 100644
--- a/Classes/Domain/Repository/LogRepository.php
+++ b/Classes/Domain/Repository/LogRepository.php
@@ -354,7 +354,7 @@ function updateInTtAddress($address, $mode, $tableUid, $salutation = '')
      * @param   int     $tableUid   externe uid
      * @param   string  $extension  mail or luxletter
      */
-    function updateInFeUsers($address, $tableUid, $extension)
+    function updateInFeUsers($address, $tableUid, $extension = 'luxletter')
     {
         $timestamp = time();
         $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('fe_users');
@@ -416,7 +416,7 @@ function updateInFeUsers($address, $tableUid, $extension)
      * @param   string  $table      tt_address or fe_users
      * @param   string  $extension  luxletter or mail
      */
-    function deleteExternalUser($uid, $mode, $dmCatArr = [], $table = 'tt_address', $extension)
+    function deleteExternalUser($uid, $mode, $dmCatArr = [], $table = 'tt_address', $extension = 'luxletter')
     {
         $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable($table);
         if ($mode == 2) {
diff --git a/Documentation/ChangeLog/Index.rst b/Documentation/ChangeLog/Index.rst
index 99edf38..e6a56f0 100644
--- a/Documentation/ChangeLog/Index.rst
+++ b/Documentation/ChangeLog/Index.rst
@@ -158,4 +158,7 @@ Version 6.2.0:
 - New setting: newsletterExtension (mail or luxletter).
 
 Version 6.3.0:
-- New action: direct unsubscribe via Mail-link and new setting: authCodeFields.
\ No newline at end of file
+- New action: direct unsubscribe via Mail-link and new setting: authCodeFields.
+
+Version 6.3.1:
+- Bugfix: Luxletter is now the default newsletter-extension - to prevent a PHP warning.
\ No newline at end of file
diff --git a/Documentation/Configuration/Index.rst b/Documentation/Configuration/Index.rst
index ce472ff..3bd099d 100644
--- a/Documentation/Configuration/Index.rst
+++ b/Documentation/Configuration/Index.rst
@@ -27,7 +27,7 @@ Properties for settings
 Property                          Data type   Description                                                           Default
 ================================= =========== ===================================================================== =================================
 table                             string      tt_address, fe_users or none (empty value) supported                  tt_address
-newsletterExtension               string      luxletter (default for fe_users) or mail (default for tt_address)
+newsletterExtension               string      luxletter (default for fe_users) or mail (default for tt_address)     empty = luxletter
 optionalFields                    string      Optional fields: see below                                            gender,firstname,lastname
 optionalFieldsRequired            string      Optional required* fields: see below
 doubleOptOut                      boolean     Enable double out out unsubscription?                                 1
diff --git a/Documentation/Localization.de_DE/ChangeLog/Index.rst b/Documentation/Localization.de_DE/ChangeLog/Index.rst
index 5744d3f..7c24cf5 100644
--- a/Documentation/Localization.de_DE/ChangeLog/Index.rst
+++ b/Documentation/Localization.de_DE/ChangeLog/Index.rst
@@ -156,4 +156,7 @@ Version 6.2.0:
 - Neue Einstellungsmöglichkeit: newsletterExtension (mail oder luxletter).
 
 Version 6.3.0:
-- Neue action: direkte Abmeldung via Mail-Link und neue setting: authCodeFields.
\ No newline at end of file
+- Neue action: direkte Abmeldung via Mail-Link und neue setting: authCodeFields.
+
+Version 6.3.1:
+- Bugfix: Luxletter ist nun die Standard Newsletter-Extension - um eine PHP-Warnung zu verhindern.
\ No newline at end of file
diff --git a/Documentation/Localization.de_DE/Configuration/Index.rst b/Documentation/Localization.de_DE/Configuration/Index.rst
index fe4e138..d97ca23 100644
--- a/Documentation/Localization.de_DE/Configuration/Index.rst
+++ b/Documentation/Localization.de_DE/Configuration/Index.rst
@@ -27,7 +27,7 @@ Settings-Einstellungen
 Feld                              Typ         Beschreibung                                                          Standard-Wert
 ================================= =========== ===================================================================== ================================
 table                             string      tt_address, fe_users oder keine Tabelle (leerer Wert) möglich         tt_address
-newsletterExtension               string      luxletter (default für fe_users) oder mail (default für tt_address)
+newsletterExtension               string      luxletter (default für fe_users) oder mail (default für tt_address)   leer = luxletter
 optionalFields                    string      Optionale Werte: siehe weiter unten                                   gender,firstname,lastname
 optionalFieldsRequired            string      Optionale erforderliche* Werte: siehe weiter unten
 doubleOptOut                      boolean     Double opt out Abmeldung einschalten?                                 1
diff --git a/README.md b/README.md
index 2a4b4ea..5359da1 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # fp_newsletter
 
-version 6.3.0
+version 6.3.1
 
 The TYPO3 extension fp_newsletter is designed to provide a newsletter subscription and unsubscription service for the 
 table tt_address which can be used by the extension mail OR for the table fe_users which can be used by luxletter or mail. 
@@ -46,4 +46,7 @@ Version 6.2.0:
 - New setting: newsletterExtension (mail or luxletter).
 
 Version 6.3.0:
-- New action: direct unsubscribe via Mail-link and new setting: authCodeFields.
\ No newline at end of file
+- New action: direct unsubscribe via Mail-link and new setting: authCodeFields.
+
+Version 6.3.1:
+- Bugfix: Luxletter is now the default newsletter-extension - to prevent a PHP warning.
\ No newline at end of file
diff --git a/ext_emconf.php b/ext_emconf.php
index 6550abf..b19a3b1 100644
--- a/ext_emconf.php
+++ b/ext_emconf.php
@@ -18,7 +18,7 @@
     'author_company' => 'fixpunkt für digitales GmbH',
     'state' => 'stable',
     'clearCacheOnLoad' => 0,
-    'version' => '6.3.0',
+    'version' => '6.3.1',
     'constraints' => [
         'depends' => [
         	'typo3' => '11.5.0-12.4.99'