Copy the widget code from Set up & customize section of your Chatra dashboard (log into Chatra or sign up if needed).
In your Bigcommerce dashboard, click on the Settings and proceed to the Live Chat section of the Advanced Settings:
Check the Other Third Party Live Chat Service box and click on the Save button:
Open the Other Third Party Live Chat Service tab:
Paste your Chatra widget code to the Live Chat Code box, choose At the top of the page as the Chat Box Location. Click on the Save button:
Open your store page to complete the installation. You should see the Chatra widget at the bottom of the page. Done!