Integrate Paypal Express Checkout Solution

As a web developer, there will surely be someday where you wish to integrate Paypal into one of your products or services. The most appropriate way is to read the documentation provided by Paypal. But reading it doesn't mean you will understand the documentation with one shot and this call for a lot of research and finding before your Paypal will work. I went through this process these few days that is why there wasn't much article written in the process.  Although it wasn't really difficult but going through the process of reading first before looking into their sample codes really wasn't the correct way of approaching this solution. Instead, looking into the sample code will definitely brings light to integrating Paypal express checkout solution (well, you still have to read a bit). In this article, i will try to demonstrate Paypal express checkout solution as simple as possible for you guys to be able to DIY.

Paypal Express Checkout

What is Paypal Express checkout solution? Paypal Express Checkout makes it easier for your customers to pay and allows you to accept PayPal while retaining control of the buyer and overall checkout flow. This means that you can integrate a payment solution with Paypal that retain most of the interaction on your website other than user login and verifying the product they are purchasing. Paypal express checkout also provides you with the ability to create recurring payment which can really eliminate the need to repurchase the exact service or product every single time. However, Paypal express checkout solution doesn't have the ability to allow your user to use credit card for purchases. Your customers must have Paypal in order to purchase with this solution. Credit card solution will only be available together with Paypal in Website Payment Pro solution. Hopefully this clear some doubt and help you select what solution you really need.

Integrate Paypal Express Checkout Solution - Step 1

Firstly, you might wonder where exactly are the correct documentation out of all the places in Paypal. You can get the documentation and Sample at the respective links. The sample is contain at the section PayPal API: Name-Value Pair Interface as i believe this will give you a better understanding on the flow of Paypal express check out solution. The sample files will required you to throw them  into your server and run (go to the browser and key in the url you have thrown the folder into) as it will simulate some of the payment flow you might want. Then you will look into the code and see how they are achieved. Please take note that localhost might not work for you as it will required you to have curl installed.

Integrate Paypal Express Checkout Solution - Step 2

Once the sample are placed into your server and you have play around, the next thing you might wonder is the exact file you will required to run your own Paypal express checkout solution. And here are the files you will only need.

  • APIError - display error
  • CallerService - main player that initial the talk
  • constants - all the required variables
  • SetExpressCheckout - display for step 1 of the process
  • GetExpressCheckoutDetails - display for step 2 of the process
  • DoExpressCheckoutPayment -  display for step 3 of the process + send final request to paypal
  • ReviewOrder - request handler for step 1 and responsible to redirect to step 2

The files i am looking at are all PHP files.  Well, the above file respective function should be self explained. The first 3 files(APIError, CallerService and Constants) are the files imported into the ReviewOrder and  DoExpressCheckoutPayment files as they are required to talk to Paypal. Once we understand this it is time to go into a more complicated stuff.

Integrate Paypal Express Checkout Solution - Step 3

To illustrate what is going on in the sample file, we will look at the following diagram provided by Paypal.

From left to right, we have 5 interfaces user will see. And two of them are display from Paypal where it is colored in blue (2nd and 3rd interface). Hence, we left with 3 interfaces which are SetExpressCheckout, GetExpressCheckoutDetails and DoExpressCheckoutPayment which is 1st, 4th and 5th interface respectively.  So we are all clear with the display files right now. Next we will need to know where ReviewOrder will appear. There are altogether 4 Calcuts as written on the diagram. The ReviewOrder will be triggered on the 2nd and 3rd Calcuts where SetExpressCheckout API and GETExpressCheckoutDetails API is being fired. Don't worry about what does these API means at the moment. Just treat them as a method that will tell Paypal what they do.

Integrate Paypal Express Checkout Solution - Step 4

I guess everyone should understand how Paypal work looking at the sample file and the explanation above.  Next i will explain some of the important things you will need to know since writing all the codes here is meaningless as they are the same for every sample files. It just makes it more confusing to read. Firstly, for each request made to Paypal, you will always see the following line in the sample file.


where $nvpstr is the name-value pair string passed into the method hash_call. What this function hash_call does it to send the request to Paypal to notify them the action you performing. In this case, SetExpressCheckout API is being performed here. There are also other API as mention previous such as GetExpressCheckoutDetails API and DoExpressCheckoutPayment API. These are the three API you will need to talk to Paypal in each stage shown on the previous diagram. So we should all clear about what does API mean that are written all over the Paypal documentation. The next important step is to know what name-value pair does each API required you to send in order for Paypal to understand you.

Integrate Paypal Express Checkout Solution - Step 5

Here we will see what does each API in the process of express checkout required. For SetExpressCheckout, you will required to have the following name-value pair in your string.

  • AMT

That is all! But in the sample it gives you more than just the above which is pretty good to understand what can be dump into the nvp string for it to display what you want on the paypal website where your user gets redirected.

For GetExpressCheckoutDetails API is pretty simple. It will just required you to have a token passed into the nvp string and this token can be retrieved via $_GET method where Paypal send it through there.

Lastly, for DoExpressCheckoutPayment API, you will need to provide the following nvp for it to work.

  • AMT

And that's it! The value forGetExpressCheckoutDetails and DoExpressCheckoutPayment API are provided by Paypal during the process while SetExpressCheckout data are given by you.


I believe the above explanations were pretty clear. But i still used quite a hell lots of time working on it *SLAP MYSELF*! This article is intended to provide any newbie on Paypal to get the hang of integrating Paypal without the need to spend time on reading and learning all about Paypal integration. However, the sample provided by Paypal is not secure and is only used to serve as a demonstration on 'how integration can be made easy'. I believe this article will be pretty useful for anyone to understand how Paypal work rather than reading few thousand words given by Paypal and never direct you to the correct sources or code (other than more documentation). Guess what? I found this Paypal Integration Wizard which is a wizard that creates all the above codes for you! :[

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