Follow the below instructions for find your BigCommerce API Keys -
Click Create API Account button.
In the Token type field, choose V2/V3 API Token. Enter a Name for the application corresponding to this account - OMS. Then copy or make note of the API path Which you have to provide in OMS intergration setup.
Under OAuth Scopes, select API resources and permissions to which your application requires access. Please check the image below and make sure all selected correctly.
Click on Save button. If it’s successful, a .txt file containing the API credentials will download to your computer and a pop-up containing the same credentials will be displayed.
Store the Client ID, Client Secret and Access Token to your computer. You can also find these API credentials including the API Path in the downloaded .txt file.
Now you can use all API details in OMS intergration process.
Please open the ticket for your enquriy.