To add as a payment gateway in NopCommerce, you can follow these steps:

  1. Log in to your NopCommerce admin panel and navigate to Configuration > Payment > Payment methods.
  2. Click on the “Add new” button and select “AuthorizeNet” from the list of available payment methods.
  3. Enter your API login ID and transaction key, which can be obtained from your account.
  4. Configure the other payment method settings as needed, such as transaction mode (test or live), payment action (authorize only or authorize and capture), and allowed countries.
  5. Save the payment method settings and test the integration by placing a test order and processing a payment through

Note: Before integrating, make sure that your NopCommerce website is using a secure HTTPS connection and that your account is set up to accept payments from your website’s domain. You may also need to configure additional security settings, such as fraud detection and prevention, depending on your business needs.