Does this simple paypal solution allow credit card

I am so confused about the services and over here the paypal website also seems to be serving up 400's and 404s.

This is how the webpage looks for customers on my site when they are ready to pay:

As far as I know, I don't have Express Checkout, but I'm not sure if I have Website Payments Pro (my company created this account).

Now I have two questions:

1- This is just the sandbox. But on the real site, does this solution that give users the opportunity to pay by credit card? I've actually successfully done a credit card transaction in the sandbox, I'm just worried because I've heard that customers can only do direct credit card transactions in PayPal Website Payments Pro. The PayPal website is overloaded with information and I can't find my way around it to answer simple questions like this.

2- Is it possible to do negative testing for transactions on this page? Such as simulating the events that the user's credit card or Paypal account doesn't have enough balance? If it is possible, and I am using the ButtonManagerAPI, then is the technique below the correct way to go about it?

I put an error code in the amount variable that is passed on to IPN via via an NVP api call, like this (lots of value pairs in the middle excluded as irrelevant):

$nvpReq = "BUTTONCODE=HOSTED&..............&L_BUTTONVAR1=amount=".$err_code

EDIT

So it appears I have PayPal Website Payments Standard, which means I cannot incorporate cannot have credit card payment forms directly on my website, but customers have to be directed to PayPal. I'm fine with that, as long as customers have the option to pay with credit cards.

The screenshot looks like PayPal Standard, which is an HTML-only (non-API) integration.

Any regular business account that can receive money can make use of the Express Checkout API.. typically by authenticating with an API USER/PWD/SIGNATURE. For businesses with programming/development resources, EC is by far the recommended way to accept PayPal payments.

If you pass SOLUTIONTYPE=Sole in the initial SetExpressCheckout call, it will accept credit cards from "guest" customers who don't have a PayPal account, similar to the Standard screenshot you're displaying above.

The main reason to choose EC over Standard is that it's a much tighter handshake between your checkout software and PayPal's servers. With Standard's HTML-only, the customer is redirected away from your site and might not return to your site after a successful transaction is committed (they may stay on paypal.com and not click to return or their browser might crash before return --- whereas with EC the return to your site is built-in before anything touches the financial system)

With the recent beta of developer.paypal.com, all new sandbox Business accounts are full Pro accounts by default. Signing up for a live Pro account would be useful if, in addition to accepting PayPal payments, you wished to create a credit card entry form directly on your own site.

Here are some EC links for programmers:

https://tryit.paypal.com/guide/ec
https://paypal-labs.com/integrationwizard/ecpaypal/main.php

The button manager API is unlikely to be useful to you. And there are ways to do negative testing with the sandbox, but it's really not an important concern when you're still deciding on a product/API.