Can someone tell me if it possible to make use of the Paypal NVP API in PHP without the use of cURL. eg. when you request the paykey.
also is the Paypal IPN feature (I'm using localhost) necessary, and what is it's function?
Sorry, but the Paypal documentation didn't answer any of these questions.
The paypal API uses the HTTP protocol to send and receive data. Thus, if you wanted, you can use any HTTP library or even write your own based on PHP sockets and use that. cURL seems like the best way to get it done though.
The IPN is a way to be notified of any transaction on your account. It sends an HTTP POST to the URL you specify, allowing you to automate your sales tracking, shipping, download link generation, etc. If you want to handle this manually, you need not use IPN.