Set up API permissions for Express Checkout

I have followed (http://www.zen-cart.com/index.php?main_page=page&id=15) to set up Express Checkout module in my zen-cart store.

When I go to step3, on the page of API Access, there is an option that I don't know what to do with it: "Accept payments from your online stores before setting up APIs / Enable Express Checkout to accept payments from your online stores right away. You can set up API permissions or credentials later. "

Here are 2 options below, what is the difference???:

1. Accept PayPal payments before API permissions or credentials are set up
2. Block payments from uncredentialed shopping carts

As I understand, in order to get payment from my store to my payPal account, I need to set up API anyway, how come there is possibility to get payments from online stores or shopping carts before you set up API permissions? In this case, how to link my PayPal and my Store?

I see 3 options:

• Option 1 - Grant API permissions to a third party to use certain PayPal APIs on your behalf.
• Option 2 - Request API credentials to create your own API username and password.
• Accept payments from your online stores before setting up APIs

As per the article you referenced, you want OPTION 2 - REQUEST API CREDENTIALS TO CREATE YOUR OWN API USERNAME AND PASSWORD

DrByte:

I see 3 options:

• Option 1 - Grant API permissions to a third party to use certain PayPal APIs on your behalf.
• Option 2 - Request API credentials to create your own API username and password.
• Accept payments from your online stores before setting up APIs

As per the article you referenced, you want OPTION 2 - REQUEST API CREDENTIALS TO CREATE YOUR OWN API USERNAME AND PASSWORD

I have already chosed Option 2 - Request API credentials ...and completed setting in zen-cart admin accordingly.

But when I click Accept payments from your online stores before setting up APIs, 2 alternative shows up:
A. Accept PayPal payments before API permissions or credentials are set up
B. Block payments from uncredentialed shopping carts

And then I have already submitted A. or B. several times, but not sure what it will cause?

If you've already set up your API credentials, then WHY are you bothering with clicking on "Accept payments from your online stores before setting up APIs"?
Ignore the "Accept payments from your online stores before setting up APIs" thing, because you've already set up API stuff. You're no longer in the "before" state.