How to Resolve Invalid Receipt Status When Verifying In-App Purchases in iOS?

Verifying In-App Purchase Receipts

In-app purchases provide a convenient way for users to acquire additional content or features within your app. To ensure transactions are legitimate, validating receipts with the App Store is crucial.

Problem:

One developer encountered difficulties verifying receipts, consistently receiving an invalid status. Despite extensive troubleshooting, the issue persisted.

Solution:

To assist, the following steps are recommended:

1. Verify Receipt Method:

   <code class="objective-c">- (BOOL)verifyReceipt:(SKPaymentTransaction *)transaction {
       // Encode receipt data
       NSString *jsonObjectString = [self encode:(uint8_t *)transaction.transactionReceipt.bytes length:transaction.transactionReceipt.length];
   
       // Construct URL for validation
       NSString *completeString = [NSString stringWithFormat:@"http://url-for-your-php?receipt=%@", jsonObjectString];
       NSURL *urlForValidation = [NSURL URLWithString:completeString];
   
       // Create HTTP request
       NSMutableURLRequest *validationRequest = [[NSMutableURLRequest alloc] initWithURL:urlForValidation];
       [validationRequest setHTTPMethod:@"GET"];
   
       // Send request and receive response
       NSData *responseData = [NSURLConnection sendSynchronousRequest:validationRequest returningResponse:nil error:nil];
       [validationRequest release];
   
       // Parse response
       NSString *responseString = [[NSString alloc] initWithData:responseData encoding: NSUTF8StringEncoding];
       NSInteger response = [responseString integerValue];
       [responseString release];
   
       // Return verification result
       return (response == 0);
   }</code>

2. Encoding Method:

   <code class="objective-c">- (NSString *)encode:(const uint8_t *)input length:(NSInteger)length {
       static char table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
   
       NSMutableData *data = [NSMutableData dataWithLength:((length + 2) / 3) * 4];
       uint8_t *output = (uint8_t *)data.mutableBytes;
   
       for (NSInteger i = 0; i < length; i += 3) {
           NSInteger value = 0;
           for (NSInteger j = i; j < (i + 3); j++) {
               value <<= 8;
   
               if (j < length) {
                   value |= (0xFF & input[j]);
               }
           }
   
           NSInteger index = (i / 3) * 4;
           output[index + 0] = table[(value >> 18) & 0x3F];
           output[index + 1] = table[(value >> 12) & 0x3F];
           output[index + 2] = (i + 1) < length ? table[(value >> 6) & 0x3F] : '=';
           output[index + 3] = (i + 2) < length ? table[(value >> 0) & 0x3F] : '=';
       }
   
       return [[[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding] autorelease];
   }</code>

3. Server-Side Validation:

   <code class="php">$receipt = json_encode(array("receipt-data" => $_GET["receipt"]));
   // NOTE: use "buy" vs "sandbox" in production.
   $url = "https://sandbox.itunes.apple.com/verifyReceipt";
   $response_json = call-your-http-post-here($url, $receipt);
   $response = json_decode($response_json);
   
   // Save the data here!
   
   echo $response->status;</code>

4. Internal Methods:

   <code class="objective-c">@interface YourStoreClass (Internal)
   - (BOOL)verifyReceipt:(SKPaymentTransaction *)transaction;
   - (NSString *)encode:(const uint8_t *)input length:(NSInteger)length;
   @end</code>

5. Additional Considerations:

   • Consider asynchronous HTTP posting due to potential request length and processing time.
   • Provide user feedback during receipt validation.

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