I want to verify the transaction receipt within my app,
Here is my code,
- (void)recordTransaction:(SKPaymentTransaction *)transaction {
    NSData *receiptData = [NSData dataWithData:transaction.transactionReceipt];
    NSString *encodedString = [Base64 encode:receiptData];
     NSURL *url = [NSURL URLWithString:@"https://sandbox.itunes.apple.com/verifyReceipt"];
    ASIFormDataRequest *request = [[ASIFormDataRequest alloc] initWithURL:url];
    [request setPostValue:encodedString forKey:@"receipt-data"];
    [request setRequestMethod:@"POST"];
    [request setDelegate:self];
    [request startAsynchronous];
}
I am getting output:
{"status":21002, "exception":"java.lang.NullPointerException"}
Can someone help me to get proper receipt verification?