diff --git a/src/Service/AnalyticsCryptoService.php b/src/Service/AnalyticsCryptoService.php
index 1646093..130c66c 100644
--- a/src/Service/AnalyticsCryptoService.php
+++ b/src/Service/AnalyticsCryptoService.php
@@ -20,7 +20,8 @@ class AnalyticsCryptoService
         $iv = random_bytes(12);
         $encrypted = openssl_encrypt($json, 'aes-256-gcm', $this->key, \OPENSSL_RAW_DATA, $iv, $tag, '', 16);
 
-        return base64_encode($iv.$tag.$encrypted);
+        // Format compatible with Web Crypto API: iv + ciphertext + tag
+        return base64_encode($iv.$encrypted.$tag);
     }
 
     public function decrypt(string $payload): ?array
@@ -30,7 +31,21 @@ class AnalyticsCryptoService
             return null;
         }
 
+        // Try JS format first: iv (12) + ciphertext_with_tag (tag is last 16 bytes)
         $iv = substr($raw, 0, 12);
+        $ciphertextWithTag = substr($raw, 12);
+
+        if (\strlen($ciphertextWithTag) >= 16) {
+            $tag = substr($ciphertextWithTag, -16);
+            $encrypted = substr($ciphertextWithTag, 0, -16);
+
+            $json = openssl_decrypt($encrypted, 'aes-256-gcm', $this->key, \OPENSSL_RAW_DATA, $iv, $tag);
+            if (false !== $json) {
+                return json_decode($json, true);
+            }
+        }
+
+        // Fallback: PHP format iv (12) + tag (16) + ciphertext
         $tag = substr($raw, 12, 16);
         $encrypted = substr($raw, 28);