为什么要使用客户/买方API凭据？

Question

I'm integrating PayPal into a client's website for the first time. I've been using seller and buyer test accounts and testing on Sandbox. I've used the seller's API credentials in creating Buy Now buttons dynamically, and these credentials are used in the NVP that goes through cURL. I'm also using the credentials in the IPN listener that does the business logic once a buyer makes a payment.

I've tested being a buyer who buys using a PayPal account and I've also tested buying the product using credit cards.

1. I'm just wondering, why do we need the buyer's API credentials? Are there are some important tests I'm missing out where these credentials are used to make API calls?

2. How can I create errors in order to take advantage of "Negative" testing, which is an option that shows up if I click on the "Profile" of one of the test sandbox accounts in the new developer interface?

I know some of these questions can be answered by looking at paypal's developer site, and I've been through its site pages over and over again, I'm asking here on SO because while PayPal is comprehensive, I don't find it clear enough for a beginner like me.

Answer 1

To answer your questions.

1. These credentials are what allow you to access the account via API call. It's an authentication method similar to using a user id and password for accessing the account, performing actions on the account and retrieving information from the account. You would not want just anyone to be able to access your account, so API credentials are used for accessing your account.
2. If you are wanting to use negative testing, refer to the developers guide. This will tell you want you need to pass to trigger specific error codes. Passing different values for such things as amount, cvv2, the address and etc will trigger different errors. As for triggering errors on the profile, you wouldn't be able to do this with negative testing, if this is what you are asking.