Paypal authentication problem !

[alhakeem2001]

I'm having a problem with setting my paypal account to work properly as when the customer reaches the checkout page there will be 2 buttons, one is the default and an extra button to checkout with paypal but when the customer clicks on that button, it takes him to the”Step 1 of 3 - Delivery Information Shipping Information: “ and then they have to chose the delivery method then they reach the page where they need to chose the payment method and there I have 3 methods :



- Save time. Check out securely.
Pay without sharing your financial information.

- Checkout with PayPal. The safer, easier way to pay.

- Credit Card
Cardholder First Name:
Cardholder Last Name:
Card Number:
Card Expiry Date:
CVV Number: (on back of the credit card)

The only method that works with me of the 3 paypal choices is the first one which it takes me to my merchant paypal page to complete the purchase process which I couldn’t test till the end because I have only one account on Paypal so I can’t pay to my self ! with second after confirming
the order at Step 2 of 3 - Payment Information page a note with a red background comes saying :

We are sorry for the inconvenience. The PayPal account authentication settings are not yet set up, or the API security information is incorrect. We are unable to complete your transaction. Please notify the store owner so they can correct this problem. (10002) 10002 Security error - Security header is not valid

With third choice after filling the info and confirming the order, at the Step 2 of 3 - Payment Information page a note comes with:

10002 Security error - Security header is not valid .

Now why the two other options didn’t work with me and whats the deferent between the first and the other two options and why I have the paypal button at the checkout page when it doesn’t take the customer to the final payment process? Any help will be appreciated .