RestorePurchases.h

#import <UIKit/UIKit.h>
#import <StoreKit/StoreKit.h>

@interface RestorePurchases : UIViewController <SKProductsRequestDelegate, SKPaymentTransactionObserver, SKRequestDelegate, UIActionSheetDelegate>


@end

RestorePurchases.m

- (IBAction)removeAds:(id)sender {
    UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:NSLocalizedString(@"Remove Ads", nil)
                                                             delegate:self
                                                    cancelButtonTitle:NSLocalizedString(@"Cancel", nil)
                                               destructiveButtonTitle:NSLocalizedString(@"Buy Remove Ads", nil)
                                                    otherButtonTitles:NSLocalizedString(@"Restore previous purchase", nil), nil];
    [actionSheet showInView:self.view];
}

#pragma mark UIActionSheetDelegate
- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    if(buttonIndex == 0) {
        //Buy
    } else if(buttonIndex == 1) {
        //Restore purchases
        [[SKPaymentQueue defaultQueue] addTransactionObserver:self];
        [[SKPaymentQueue defaultQueue] restoreCompletedTransactions];
    }
}

- (void) paymentQueueRestoreCompletedTransactionsFinished:(SKPaymentQueue *)queue {
    NSLog(@"received restored transactions: %lu", (unsigned long)queue.transactions.count);
    if(queue.transactions.count > 0) {
        for (SKPaymentTransaction *transaction in queue.transactions) {
            NSURL *receiptURL = [[NSBundle mainBundle] appStoreReceiptURL];
            NSData *receipt = [NSData dataWithContentsOfURL:receiptURL];
            
            if (receipt) {
                NSString *receiptDataString = [receipt base64EncodedStringWithOptions:0];
                NSLog(@"Purchase reference:%@",receiptDataString);
                //Do whatever with the purchase
            }
            
            [[SKPaymentQueue defaultQueue] finishTransaction:transaction];
        }
        //Restore succeeded
    } else {
        //Show error
    }
}