Index: /controller/wpsg_SystemController.class.php
===================================================================
--- /controller/wpsg_SystemController.class.php	(revision 7400)
+++ /controller/wpsg_SystemController.class.php	(revision 7401)
@@ -91,14 +91,12 @@
 		{
 
-			if(wpsg_isSizedString($sanitize_type))
-			{
+			if (wpsg_isSizedString($sanitize_type)) {
 
 				array_unshift($sanitize_params, $value);
 				array_unshift($sanitize_params, $sanitize_type);
-
+ 
 				$value = call_user_func_array("wpsg_sanitize", $sanitize_params);
 
-				if($value === false)
-				{
+				if ($value === false) {
 
 					$value = $this->get_option($key);
Index: /lib/functions.inc.php
===================================================================
--- /lib/functions.inc.php	(revision 7400)
+++ /lib/functions.inc.php	(revision 7401)
@@ -530,6 +530,7 @@
 			"sanitize_hex_color" => "str",
 			"sanitize_hex_color_no_hash" => "str",
-			"sanitize_html_class" => "str",
+			"sanitize_html_class" => "str",			
 			"sanitize_key" => "int",
+			'sanitize_wpsg_taxkey' => 'taxkey',
 			"sanitize_meta" => "int", // gettype($meta_key) === "int"
 			"sanitize_mime_type" => "str",
@@ -543,9 +544,9 @@
 			"wpsg_txt_tbl" => "txt_tbl"
 		);
-
-		if(!array_key_exists($type, $validTypes)) return wpsg_xss($primary);
-		if(!function_exists($type) && strpos($type, "wpsg_") === false)
+ 		 
+		if (!array_key_exists($type, $validTypes)) return wpsg_xss($primary);
+		if (!function_exists($type) && strpos($type, "wpsg_") === false)
 			throw new \wpsg\Exception("Function $type does not exists in the WordPress function pool.");
-
+				 
 		# Validation (and Sanitization for type txt_tbl)
 		switch($validTypes[$type])
@@ -555,7 +556,21 @@
 			case "str":
 				if(gettype($primary) !== "string" || is_numeric($primary))
-					$err = __("Bitte ÃŒberprÃŒfen sie folgende Eingabe: ");
+					$err = __("Bitte ÃŒberprÃŒfen sie folgende Eingabe: ", "wpsg");
 				break;
 
+			case "taxkey":
+				 
+				$primary = strtolower($primary);
+				
+				if (!in_array($primary, ['0', 'a', 'b', 'c', 'd'])) {
+					
+					$GLOBALS['wpsg_sc']->addBackendError(__('ÜberprÃŒfen Sie den Mehrwertsteuersatz, die Eingabe war ungÃŒltig.', 'wpsg'));
+					
+					return false;
+					
+				}  
+				
+				break;
+				
 			// Asked for an integer
 			case "int":
@@ -641,17 +656,23 @@
 		}
 
-		# Sanitization
-		try{
-
-			// If a float/double value is wanted
-			if($validTypes[$type] !== "int" && !in_array("isFloat", $params) || $err !== false)
-				$sanitized_val = call_user_func_array($type, $params);
-			else if(in_array("isFloat", $params))
-				$sanitized_val = sanitize_text_field($prefix.wpsg_ff($fPrimary));
-			else
-				$sanitized_val = sanitize_text_field($prefix.$nPrimary);
-
-		} catch(Exception $e) {
-			throw new \wpsg\Exception($e->getMessage(), $e->getCode());
+		# Sanitization WP Funktion
+		if (strpos($type, "wpsg_") === false) {
+			
+			try {
+	
+				// If a float/double value is wanted
+				if($validTypes[$type] !== "int" && !in_array("isFloat", $params) || $err !== false)
+					$sanitized_val = call_user_func_array($type, $params);
+				else if(in_array("isFloat", $params))
+					$sanitized_val = sanitize_text_field($prefix.wpsg_ff($fPrimary));
+				else
+					$sanitized_val = sanitize_text_field($prefix.$nPrimary);
+	
+			} catch(Exception $e) {
+				
+				throw new \wpsg\Exception($e->getMessage(), $e->getCode());
+				
+			}
+			
 		}
 
Index: /mods/wpsg_mod_paypal.class.php
===================================================================
--- /mods/wpsg_mod_paypal.class.php	(revision 7400)
+++ /mods/wpsg_mod_paypal.class.php	(revision 7401)
@@ -94,5 +94,5 @@
 			$this->shop->update_option('wpsg_mod_paypal_hint', $_REQUEST['wpsg_mod_paypal_hint'], false, false, "text_field");
 			$this->shop->update_option('wpsg_mod_paypal_gebuehr', $_REQUEST['wpsg_mod_paypal_gebuehr'], false, false, "key", ["isFloat"]);
-			$this->shop->update_option('wpsg_mod_paypal_mwst', $_REQUEST['wpsg_mod_paypal_mwst'], false, false, "key");
+			$this->shop->update_option('wpsg_mod_paypal_mwst', $_REQUEST['wpsg_mod_paypal_mwst'], false, false, "wpsg_taxkey");
 			
 			// Vor dem CreateWebHook
Index: /mods/wpsg_mod_paypalapi.class.php
===================================================================
--- /mods/wpsg_mod_paypalapi.class.php	(revision 7400)
+++ /mods/wpsg_mod_paypalapi.class.php	(revision 7401)
@@ -99,5 +99,5 @@
 			
 			$this->shop->update_option('wpsg_mod_paypalapi_gebuehr', $_REQUEST['wpsg_mod_paypalapi_gebuehr'], false, false, "key", ["isFloat"]);
-			$this->shop->update_option('wpsg_mod_paypalapi_mwst', $_REQUEST['wpsg_mod_paypalapi_mwst'], false, false, "key");
+			$this->shop->update_option('wpsg_mod_paypalapi_mwst', $_REQUEST['wpsg_mod_paypalapi_mwst'], false, false, "wpsg_taxkey");
 			$this->shop->update_option('wpsg_mod_paypalapi_mwstland', $_REQUEST['wpsg_mod_paypalapi_mwstland'], false, false, "key");