From 1f235015bab30920f86846697e1a2fbb7e273af9 Mon Sep 17 00:00:00 2001
From: Wei Zang <richzw@gmail.com>
Date: Mon, 5 Feb 2024 16:02:19 +0800
Subject: [PATCH] docs(readme): add notes to app store server api on readme

---
 README.md | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/README.md b/README.md
index ece1733..77af307 100644
--- a/README.md
+++ b/README.md
@@ -101,6 +101,15 @@ func main() {
 
 ### In App Store Server API
 
+**Note**
+- The App Store Server API differentiates between a sandbox and a production environment based on the base URL:  
+  - Use https://api.storekit.itunes.apple.com/ for the production environment.
+  - Use https://api.storekit-sandbox.itunes.apple.com/ for the sandbox environment.
+- If you're unsure about the environment, follow these steps:
+  - Initiate a call to the endpoint using the production URL. If the call is successful, the transaction identifier is associated with the production environment.
+  - If you encounter an error code `4040010`, indicating a `TransactionIdNotFoundError`, make a call to the endpoint using the sandbox URL.
+  - If this call is successful, the transaction identifier is associated with the sandbox environment. If the call fails with the same error code, the transaction identifier doesn't exist in either environment.
+
 - GetTransactionInfo
 
 ```go