diff --git a/Helper/Checkout.php b/Helper/Checkout.php
index 3c9a2bb..33ccb45 100644
--- a/Helper/Checkout.php
+++ b/Helper/Checkout.php
@@ -461,7 +461,7 @@ private function checkFieldValidity($field, $regex, $fieldName, $addressType, $m
                 return;
             }
 
-            $arr = str_split($invalidChars);
+            $arr = mb_str_split($invalidChars);
             $invalidChars = '';
             foreach ($arr as $char) {
                 $invalidChars .= '<b>' . $char . '</b> ';
diff --git a/composer.json b/composer.json
index 37f7f09..1aa9329 100644
--- a/composer.json
+++ b/composer.json
@@ -2,8 +2,9 @@
 	"name" : "lyranetwork/module-payzen",
 	"description" : "PayZen payment platform integration for Magento 2",
 	"require" : {
-		"php" : "~7|~8"
-	},
+		"php" : "~7.4|~8",
+      	"ext-mbstring": "*"
+    },
 	"type" : "magento2-module",
 	"version" : "2.10.0",
 	"license" : "OSL-3.0",