1. Log in to PayPal.
2. Navigate to the following:
Settings > Account Settings > Website payments under Products and Services > Click the Update link under API Access.
3. Under Custom checkout experience section, click on Manage API credentials link under NVP/SOAP API integration (Classic) option:
If you haven’t set it up before, you will be asked the following:
Choose Request API signature and click the Agree and Submit button.
On the next page, copy the API Username, Password, and Signature generated. Click the Done button if you’re done.
You will have to remove existing credentials if you want to generate a new one. We, however, do not recommend removing this if you have existing integrations that use the credentials.
We highly recommend that you keep your API credentials safe for future reference.