1. Login to your LR's account
Click menu Merchant Tools at top of page.

After you see that screen, click Create API
 
2. Data API

API Name : Type your desired API name
IP : list IP that allowed to access your IP (optional)
Security Word : Password for accessing your API
Click Enabled and type in your daily maximum spend value. 0 means unlimited.
Type in your Master Key account and click Submit.
 
3. API Created

If you have success create New Api, your screen will show the above picture.