diff --git a/main/api.php b/main/api.php
index 194a27d..f0874a6 100644
--- a/main/api.php
+++ b/main/api.php
@@ -62,10 +62,18 @@ if (!$username || !$message) {
 }
 
 try {
+    $stmt = $db->prepare('SELECT id FROM users WHERE username = ?');
+    $stmt->execute([$username]);
+    if ($stmt->fetch()) {
+        http_response_code(400);
+        die(json_encode(['error' => 'Username already registered']));
+    }
+
     $stmt = $db->prepare('INSERT INTO messages (username, message, signature, is_encrypted) VALUES (?, ?, ?, ?)');
     $stmt->execute([$username, $message, $signature, $is_encrypted]);
     echo json_encode(['success' => true]);
 } catch (Exception $e) {
+    error_log("API Error: " . $e->getMessage());
     http_response_code(500);
     echo json_encode(['error' => 'Server error']);
 } 
\ No newline at end of file