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Log into your Mangeto admin portal.
Navigate to System => Webservices => SOAP/XMP-RPC => Roles.
Create a new role as OmniParcel
Select Role Resources
Grant access to Sales and Directory as shown below.
Navigate to System => Webservices => SOAP/XMP-RPC => Users
Create a new user as below. You can change the values below to suit your needs. The API Key is the password.
Select User Role. Add user to the newly created OmniParcel role.
Change Setting System => Configuration => Services => Magento Core API.
To configure the app in OmniParcel, follow these steps above.