The system should work integrated with Paypal and obtain User, Password, and Signature data from Paypal. To save Paypal settings to Options Panel, you should obtain this information from the Paypal control panel first. Please follow the steps indicated below after logging in to Paypal for this information.

If you will perform these processes under a test environment, please use the PayPal sandbox control panel.

*The feature is only available for Business accounts.

To request API Signature or Certificate credentials for your PayPal account:

  1. Log in to your PayPal Live or Sandbox account.
  2. Go to your Account Settings.
  3. In the “API access” section, click Update.
  4. Under “NVP/SOAP API integration (Classic),” click Manage API credentials.
    • If you have already generated an API Signature, then View API Signature appears. Click that option to view or remove your existing API Signature.
    • Note: If you are prompted to verify your PayPal account, then follow the on-screen instructions.
  5. Select one of the following options, then click Agree and Submit.
    • Request API Signature – Select for API Signature authentication.
  6. PayPal generates your API credentials as follows:
    • API Signature credentials include an API Username, API Password, and Signature, which does not expire. These values are hidden by default for added security. Click Show/Hide to toggle them on and off. When finished, click Done.

Add the recorded User / Password and Signature to the Options panel > Frontend Upload System > Paypal section.

Source: https://www.paypal.com/us/smarthelp/article/how-do-i-request-api-signature-or-certificate-credentials-faq3196