Thursday, 11 June 2015

PayPal for C# - ASP.NET

Index

Introduction

PayPal is probably one of the first things that gets mentioned once you start discussion on online payments. It’s not so without reason – in 2008, PayPal moved over 60 billion dollars between accounts which is, you’ll agree, a respectable amount. And also, all trends show that this growth will continue – with huge number of new accounts (over 184 million accounts in 2008 compared to 96.2 million in 2005), with a new platform named PayPal X, and with more cool applications that involve paying (like Twitpay), you can bet that PayPal is here to stay. So, how can you join the whole PayPal Development movement?
Unfortunately, I would say – not so easily. When I first started with PayPal integration - it was hard, really hard. If you wish to see what I mean, just jump to the PayPal Developer Center. There is no way you’ll easily fish out what you need from that site if you are a PayPal newbie; simply - there are too many links, too many resources, and too many mixings of important and not-so-important information. So, how should you start?

Getting Started with PayPal

To those who really want to get into PayPal, and are willing to shell out some buck, I would recommend the Pro PayPal E-Commerce book - that’s how I eventually got into understanding the concepts behind PayPal integration. For those who are not so eager to pay – don’t worry, that’s why this article is here... I'll go over most of the stuff that book covers, but in a more brief and concise manner.
First and foremost - understanding what kinds of integration PayPal offers is, I would say, the most important thing in order to successfully start your development journey. A common mistake, that happened to me also, is to start at once with the PayPal API and Express Checkout. I mean it’s natural - we are developers, and when they tell us to integrate with something, the first thing we look for is the SDK & API… the PayPal API comes up as a result… we say “That’s it” to ourselves… and start working. The problem is – the majority of payment scenarios can be handled with a way simpler approach - HTML forms that are part of the Website Payments Standard.
So, without further ado, here is a classification of PayPal integrations:
  • Website Payments Standard (HTML)
  • Postpayment Processing
    • AutoReturn
    • Payment Data Transfer (PDT)
    • Instant Payment Notification (IPN)
  • PayPal API
    • Express Checkout
    • Direct Payment (Website Payments Pro)
  • Payflow Gateway
Items in classification are also ordered in a way I would suggest for everyone to follow. So, if you are new to PayPal – first learn all of the options that you have with the Website Payments Standard (HTML). Then, if you need to add some basic post-payment processing, see if Auto-Return or PDT will solve your problem… if not, IPN is a more robust option you have at your disposal.
The next level would involve the PayPal API and implementing the Express Checkout, which is the most flexible PayPal integration solution. And finally, if you long for the ability to directly process credit cards on your website, you’ll pay a monthly fee to PayPal and implement Direct Payment (effectively getting what is called Website Payments Pro).
The last item from our classification - the Payflow Gateway is, on the other hand, a different beast. It doesn’t “update the stack” in a way the previously mentioned technologies do. It is a solution aimed specifically at those businesses that have/want an Internet Merchant Account (IMA) and just need the payment gateway. In order to keep the article consistent, I’ll skip explaining the details of the Payflow Gateway. However, if you have any questions related to it, feel free to leave a message in the comments section and I’ll try to answer.
That said, let’s get to setting up a test PayPal account, and then we’ll delve deeper into describing the mentioned integrations.

Website Payments Standard (HTML)

In this section, I'll provide you with a number of examples that will show how to create your own HTML form for receiving money over PayPal. You'll see how to use different variables in order to influence payment details. Before we delve into details, let's take a look at the two most basic variables:
  • form's action attribute - in most cases, it should be https://www.paypal.com/cgi-bin/webscr. If you are using Sandbox for testing payments, you'll change it to https://www.sandbox.paypal.com/cgi-bin/webscr - effectively, you just insert the word sandbox into the URL (this is also true for some other integrations; e.g., the PayPal API). For upcoming examples, I won't be using the Sandbox URL because most of you would just get that "Login to use the PayPal Sandbox features" screen (look up for the image).
  • form's business child - I'll use youremailaddress@yourdomain.com for most examples; if you copy-paste the code, you'll want to replace that with the email of your PayPal account.

Basic Payment

OK, let’s say you have an opened PayPal account and you just wish to be able to accept a $10 payment for a painting you are selling through your site. Just insert the following HTML into your page and you are set to go:
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">

    <input type="hidden" name="cmd" value="_xclick" />
    <input type="hidden" name="business" value="youremailaddress@yourdomain.com" />

    <input type="hidden" name="item_name" value="My painting" />
    <input type="hidden" name="amount" value="10.00" /> 
    <input type="submit" value="Buy!" />

</form>

Shipping & Handling

The next thing that comes to mind is that you'll wish to add shipping and/or handling fees to your form. It's easy - just add more parameters:
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">

    <input type="hidden" name="cmd" value="_xclick" />
    <input type="hidden" name="business" value="youremailaddress@yourdomain.com" />

    <input type="hidden" name="item_name" value="My painting" />
    <input type="hidden" name="amount" value="10.00" />

    <input type="hidden" name="shipping" value="3.00" /> 
    <input type="hidden" name="handling" value="2.00" />

    <input type="submit" value="Buy with additional parameters!" />
</form>

Donations & Textual Links

If you aren't selling anything but rather accepting donations for some cause - you'll just need to change the value of the cmd variable to _donations. If we combine this with a common requirement to have a hyperlink instead of a button - we get the following URL (of course, you can use this method of URL creation for other PayPal payment types):
  • https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=youremailaddress@yourdomain.com&item_name=Save Polar Bears!&amount=10.00

Conclusion

My hope is that this article gave you good overview of PayPal integration options. If it did that, I'll be at peace - as once you have an understanding of the concepts laid out in this article, you'll easily fetch the needed details from the provided links. Sure, there are some topics we haven't touched, like Encrypted Website Payments,PayPal API Certificates, or Payflow Gateway, but I think you can tackle even that on your own once you fully understand all things written here.
If you get stuck on anything, I suggest that you first visit the PayPal Developer Community and ask your question in the appropriate forum. A number of great, knowledable developers monitor those forums, and it's highly probable that you'll receive an answer to almost any PayPal issue within an hour. I also have an account on that site (lepipele) and try to answer questions whenever I have time; so feel free to send me a private message if you drop by or run into trouble.
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