diff --git a/BuyPass.com-CA.md b/BuyPass.com-CA.md
index 7556ed2..b0d18fb 100644
--- a/BuyPass.com-CA.md
+++ b/BuyPass.com-CA.md
@@ -8,11 +8,35 @@ https://www.buypass.com/ssl/resources/go-ssl-technical-specification
 
 Usage:
 
+First time register account with an email, the mail is required by buypass.com
+
+```sh
+acme.sh --server https://api.buypass.com/acme/directory \
+        --register-account  --accountemail me@example.com
+```
+
+
+Then you can issue cert now.
+
 ```sh
 acme.sh --server https://api.buypass.com/acme/directory  \
-         --issue -d example.com -d www.example.com .....
+         --issue -d example.com -d www.example.com ..... \
+         --days 170
 ```
 
+Since buypass cert has 180 days lifetime, so we specify `--days 170` for acme.sh to renew the cert at the 170 th day.
+If you don't specify days, it will renew at 60 days by default.
+
+
+Once issued,  you can renew the cert without `--server` parameter.
+
+```sh
+acme.sh --renew -d example.com
+```
+
+Don't worry, all the certs will be automatically renewed as usual. 
+
+
 
 1. It only supports ACME v1,  no wildcard cert.
 2. It has 180 days lifetime.