To request API Signature credentials for your PayPal account:
Click the Settings icon next to "Log out."
Click Account access under "Account & Security" on the left of the page.
In the "API access" section, click Update.
Under "NVP/SOAP API integration," 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.If you have already generated an API Certificate, then View API Certificate appears. Click that option to view or remove your existing API Certificate.Note: If you are prompted to verify your PayPal account, then follow the on-screen instructions.
Select one of the following options, then click Agree and Submit.Request API Signature – Select for API Signature authentication.Request API Certificate – Select for API Certificate authentication.
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.API Certificate credentials include an API Username, API Password, and Certificate, which expires automatically after three years. Click Download Certificate to save the API Certificate to your desktop.