diff --git a/lighter/signer_client.py b/lighter/signer_client.py
index 1bfe202..ddeee75 100644
--- a/lighter/signer_client.py
+++ b/lighter/signer_client.py
@@ -297,7 +297,7 @@ def __init__(
             nonce_management_type=nonce_manager.NonceManagerType.OPTIMISTIC,
     ):
         self.url = url
-        self.chain_id = 304 if "mainnet" in url else 300
+        self.chain_id = 304 if ("mainnet" in url or "api" in url) else 300
 
         self.validate_api_private_keys(api_private_keys)
         self.api_key_dict = api_private_keys