diff --git a/mnemo_cards_backend/lib/api/v2/auth_api_v2.dart b/mnemo_cards_backend/lib/api/v2/auth_api_v2.dart
index b393e66..1568a76 100644
--- a/mnemo_cards_backend/lib/api/v2/auth_api_v2.dart
+++ b/mnemo_cards_backend/lib/api/v2/auth_api_v2.dart
@@ -238,21 +238,29 @@ class AuthApiV2 {
   Future<Response> authenticateTelegramWebApp(Request request) async {
     try {
       final body = await request.readAsString();
+      log('Telegram Web App auth request body: ${body.length} chars', name: 'AuthApiV2');
+      
       final json = jsonDecode(body) as Map<String, dynamic>;
       final initData = json['initData'] as String?;
 
       if (initData == null || initData.isEmpty) {
+        log('Telegram Web App auth: initData is null or empty', name: 'AuthApiV2');
         return _badRequest('Telegram Web App init data is required');
       }
 
+      log('Telegram Web App auth: initData received, length: ${initData.length}', name: 'AuthApiV2');
+
       // Use the existing telegram utils to get user ID
       final telegramUtils = TelegramUtils();
       final userData = await telegramUtils.getUserId(initData);
 
       if (userData == null) {
-        return _badRequest('Invalid Telegram Web App data');
+        log('Telegram Web App auth: getUserId returned null - validation failed', name: 'AuthApiV2');
+        return _badRequest('Invalid Telegram Web App data: validation failed');
       }
 
+      log('Telegram Web App auth: userData extracted, userId: ${userData.id}', name: 'AuthApiV2');
+
       // Find or create user based on telegram user ID
       var (user, _) = await _userManager.createOrGetUser(
         externalId: userData.id,
diff --git a/mnemo_cards_backend/lib/user/telegram.dart b/mnemo_cards_backend/lib/user/telegram.dart
index 1bdbc8a..9dc38ab 100644
--- a/mnemo_cards_backend/lib/user/telegram.dart
+++ b/mnemo_cards_backend/lib/user/telegram.dart
@@ -8,6 +8,8 @@ class TelegramUtils {
 
   /// Validates the data received from the Telegram web app
   /// Following the Python implementation exactly
+  /// 
+  /// [initData] should be URL-encoded (as received from Telegram Web App)
   bool checkValidateInitData(String hashStr, String initData, String token,
       {String cStr = "WebAppData"}) {
     try {
@@ -35,30 +37,49 @@ class TelegramUtils {
       final dataCheck = crypto.Hmac(crypto.sha256, secretKey.bytes)
           .convert(utf8.encode(dataString));
 
+      final calculatedHash = dataCheck.toString();
+      final isValid = calculatedHash == hashStr;
+      
+      if (!isValid) {
+        log('checkValidateInitData: hash mismatch. Expected: ${hashStr.substring(0, hashStr.length > 20 ? 20 : hashStr.length)}..., Got: ${calculatedHash.substring(0, calculatedHash.length > 20 ? 20 : calculatedHash.length)}...');
+      }
+      
       // Compare hex digests
-      return dataCheck.toString() == hashStr;
-    } catch (e) {
+      return isValid;
+    } catch (e, s) {
+      log('checkValidateInitData error: $e', error: e, stackTrace: s);
       return false;
     }
   }
 
   Future<({String id, String? username})?> getUserId(String initialData) async {
     try {
+      log('getUserId: initialData length: ${initialData.length}');
       final tgWebAppData = Uri.decodeComponent(initialData);
+      log('getUserId: decoded data length: ${tgWebAppData.length}');
+      
       // Extract hash from the data
       final hashMatch = RegExp(r'hash=([^&]+)').firstMatch(tgWebAppData);
       if (hashMatch == null) {
+        log('getUserId: hash not found in data');
         return null;
       }
       final hash = hashMatch.group(1)!;
+      log('getUserId: hash extracted: ${hash.substring(0, hash.length > 20 ? 20 : hash.length)}...');
+      
       // Validate using the new method
-      if (!checkValidateInitData(hash, tgWebAppData, _botToken)) {
+      // Note: checkValidateInitData expects the original URL-encoded data
+      // (as received from Telegram Web App), so we pass initialData, not tgWebAppData
+      if (!checkValidateInitData(hash, initialData, _botToken)) {
+        log('getUserId: validation failed');
         return null;
       }
+      log('getUserId: validation passed');
 
       // Extract user ID from user parameter
       final userMatch = RegExp(r'user=([^&]+)').firstMatch(tgWebAppData);
       if (userMatch == null) {
+        log('getUserId: user parameter not found');
         return null;
       }
 
@@ -67,10 +88,13 @@ class TelegramUtils {
       final userId = userData['id']?.toString();
       final username = userData['username']?.toString();
       if (userId == null) {
+        log('getUserId: user ID is null in user data');
         return null;
       }
+      log('getUserId: successfully extracted userId: $userId');
       return (id: userId, username: username);
-    } catch (e) {
+    } catch (e, s) {
+      log('getUserId error: $e', error: e, stackTrace: s);
       return null;
     }
   }