The first payment gateway I dealed with was PayPal. At that moment,
I found it sucks, very tedious to integrate into iOS platform.
Until now, I need to work with iPay88, which
has no native iOS SDK, and the process even more tedious than PayPal.
I share this because of the toughness & not easy to find any
resources on web. Hope you enjoy.

1. Register a merchant account with iPay88

You will get Merchant Code and Merchant Key.

After that, submit a request URL to iPay88 support. Where the request
URL is the page that you submit to iPay88 site, you will know later.

2. Create a page that support submit payment info to iPay88

Create a page like below (just an example).

payment.php

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<!DOCTYPE html>
<html>
    <head>
        <title>Payment...</title>
    </head>
    <body>
        <h1>Processing Payment...</h1>
        <form method="POST" action="https://www.mobile88.com/epayment/entry.asp" id="frm-submit">
            <p>If this page does not redirect to payment gateway in seconds, please click RETRY button below</p>
            <button type="Submit">RETRY</button>
            <input name="RefNo" type="hidden" value="REF000001">
            <input name="Amount" type="hidden" value="1.00">
            <input name="Signature" type="hidden" value="wsE29QS6EaqI7izfDIRPv6ku/MA=">
            <input name="ProdDesc" type="hidden" value="Buy RM1.00 credit">
            <input name="UserName" type="hidden" value="Js Lim">
            <input name="UserEmail" type="hidden" value="js@lim.com">
            <input name="UserContact" type="hidden" value="0123456789">
            <input name="MerchantCode" type="hidden" value="M00001">
            <input name="Currency" type="hidden" value="MYR">
            <input name="ResponseURL" type="hidden" value="http://mysite.com/response.php">
            <input name="BackendURL" type="hidden" value="http://mysite.com/backend.php">
        </form>
        <script type="text/javascript">
            setTimeout(function() {
                document.getElementById('frm-submit').submit();
            }, 100);
        </script>
    </body>
</html>

The Signature has a formula to generate, will be provided from iPay88

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<?php
function iPay88_signature($ref_no, $amount) {
    $key = 'apple';
    $code = 'M00001';
    $currency = 'MYR';
    $source = sprintf('%s%s%s%s%s', $key, $code, $ref_no, $amount, $currency);
    return base64_encode(hex2bin(sha1($source)));
}

function hex2bin($hexSource) {
    $bin = '';
    for ($i=0;$i<strlen($hexSource);$i=$i+2) {
        $bin .= chr(hexdec(substr($hexSource,$i,2)));
    }
    return $bin;
}

A hint here, if your amount is

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<input name="Amount" type="hidden" value="1.00">

then your signature source must be appleM00001REF000001100MYR

if amount is

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<input name="Amount" type="hidden" value="1">

then your signature source must be appleM00001REF0000011MYR

If you notice that all the inputs are hardcoded, please don’t do this
to your site, you can change to variable from query string. e.g.

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<input name="RefNo" type="hidden" value="<?php echo $_REQUEST['ref']; ?>">

Then you access in browser: http://mysite.com/payment.php

So in this case, the request URL is http://mysite.com/payment.php

But wait a minute, during the development, the URL should be localhost.
Don’t worry, we can use virtual host here, you can refer this in my other
blog post
section 3. Make sure you put the real url to /etc/hosts

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127.0.0.1        mysite.com

So when you access http://mysite.com, you are not refering to the live site,
but the development site in your local machine, now you can test with
iPay88.

This cannot be done in cURL

I have tried using cURL as well, in fact it need to be a POST request in a webpage form.

3. Create a response handler

response.php

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<?php
if (isset($_REQUEST['ErrDesc'])) {
    redirect('failure.php');
}
if (isset($_REQUEST['Signature']) && $_REQUEST['Signature'] != $my_signature) {
    // NOTE that $my_signature you can store it in session before submit the form to iPay88
    redirect('failure.php'); // for security purpose
}

// store the info returned by iPay88, you will get this in the document provided by iPay88

// after process everything, redirect to success page
redirect('success.php');

function redirect($url) {
    header('Location: ' . $url);
    exit;
}

The file above will be a POST request, if you don’t want to use $_REQUEST, you can use $_POST

Bare in mind (Updated: May 12, 2015)

Please take note on the backend.php

Sometime, there are some weird issue that may caused the response.php not working correctly. Thus, backend.php is needed here (I have faced the issue with CIMB click).

The backend.php will not work if you check for login session. e.g.

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<?php
if (is_loggedin()) exit; // will exit here

// code won't execute
...

That means you cannot deal with any session here (backend.php)

4. Create a success & failure page

success.php

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<button type="button" onclick="window.location.href='com.mysite.myapp://successClicked';">Done</button>

failure.php

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<button type="button" onclick="window.location.href='com.mysite.myapp://closeClicked';">Close</button>

See com.mysite.myapp? Is this weird to you? If you have use Waze API
you will see waze://?q=<address search term> this, waze:// is the custom scheme that only
use in Waze app. Same to this, com.mysite.myapp:// is only use in this app

5. Show the page above in your app using UIWebView

Create a custom web view to handle payment

PaymentWebViewController.m

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#import "PaymentWebViewController.h"

@interface PaymentWebViewController ()

@property (nonatomic, weak) UIWebView *webView;
@property (nonatomic, strong) UIWebView *popupWebView;

@end

@implementation PaymentWebViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // add in a refresh button
    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh target:self action:@selector(refreshButtonTapped:)];
    
    UIWebView *webView = [[UIWebView alloc] initWithFrame:self.view.bounds];
    webView.autoresizingMask = UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleTopMargin;
    webView.delegate = self;
    [self.view addSubview:webView];
    _webView = webView;
    

    NSDictionary *params = @{
                             @"ref": @"REF000001"
                             , @"amount": @"1.00"
                             // ...
                             }
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://mysite.com/payment.php?%@", [self httpBuildQuery:params]]]];
    [_webView loadRequest:request];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (NSString *)httpBuildQuery:(NSDictionary *)params
{
    NSMutableArray *parts = [NSMutableArray array];
    for (id key in params) {
        id value = params[key];
        
        NSString *keyString = [NSString stringWithFormat:@"%@", key];
        NSString *valueString = [NSString stringWithFormat:@"%@", value];
        
        NSString *part = [NSString stringWithFormat: @"%@=%@", [keyString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding], [valueString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
        [parts addObject: part];
    }
    return [parts componentsJoinedByString: @"&"];
}

- (void)refreshButtonTapped:(id)sender
{
    [_webView reload];
}

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    // Update: May 12, 2015
    // a hack to solve the Maybank2u TAC popup window issue
    if ([request.URL.path containsString:@"m2uTACProcess.do"]) {

        // init a new webview (as a popup)
        _popupWebView = [[UIWebView alloc] initWithFrame:CGRectMake(0, 0, 280, 400)];
        [_popupWebView loadRequest:request];
        
        // show it in a popup, I tested with https://github.com/rnystrom/RNBlurModalView

        return NO;
    }

    if ([[request.URL scheme] isEqual:@"com.mysite.myapp"]) {
        NSArray *component = [request.URL.description componentsSeparatedByString:@"://"];
        if ([component[1] isEqual:@"closeClicked"]) { // com.mysite.myapp://closeClicked
            // action to perform after payment failed
        }
        if ([component[1] isEqual:@"successClicked"]) { // com.mysite.myapp://successClicked
            // action to perform after success
        }
        return NO;
    }
    return YES;
}
@end

See com.mysite.myapp again? We detect if the URL scheme is com.mysite.myapp, then
perform some action.

When the time your app open this web view, you will see iPay88 page. The whole integration is done.