1. Log into the store.
2. Go to Advanced Settings.
3. Click API Accounts.
4. Click Create API Account.
5. Type the name of the user in the Username box.
6. There you will find API Path box. Copy its value.
7. Click Content - modify, Checkout Content - modify, Customers - modify, Customers Login - login, Information & Settings - modify, Marketing - modify, Orders - modify, Order Transactions - modify, Products - modify, Themes - modify, Carts - modify.
8. Click the Save button. There will appear a window BigCommerce API Credential with Client ID, Client Secret and Access Token.
9. Add BigCommerce store to your API2Cart account, using credential you've got in steps 6 and 8.