POST request to obtain customized MercadoPago's payment URL

MercadoPago.m

@implementation MercadoPago

-(NSString *) generateMercadoPagoURL:{
    
    NSMutableURLRequest *request = nil;
    NSError *errorReturned = nil;
    NSURLResponse *theResponse =[[NSURLResponse alloc]init];
    
    //we build the dictionary with the post's parameters
    NSMutableDictionary *aDictionary = [[NSMutableDictionary alloc] init];
    [aDictionary setObject:@"your_store_acc_id" forKey:@"acc_id"];
    [aDictionary setObject:@"your_store_account_token" forKey:@"token"];
    [aDictionary setObject:@"http://jonathanwiesel.com/success" forKey:@"url_succesfull"];
    [aDictionary setObject:@"VEN" forKey:@"currency"];
    [aDictionary setObject:@"Jonathan" forKey:@"cart_name"];
    [aDictionary setObject:@"Wiesel" forKey:@"cart_surname"];
    [aDictionary setObject:@"jonathanwiesel@gmail.com" forKey:@"cart_email"];
    
    [aDictionary setObject:@"10000" forKey:@"price"];
    [aDictionary setObject:@"10000234R" forKey:@"item_id"];
    [aDictionary setObject:@"Ticket out of here" forKey:@"name"];
    
    
    
    
    NSMutableString *post= [[NSMutableString alloc] init];
    
    //we check for special characters in each parameter and build the post string
    for (NSString* key in aDictionary) {
        
        NSString *strValue = [NSString stringWithFormat:@"%@",[aDictionary objectForKey:key]];
        strValue = [strValue stringByReplacingOccurrencesOfString:@"/" withString:@"%2F"]; //found in URLs
        strValue = [strValue stringByReplacingOccurrencesOfString:@"%" withString:@"%25"]; //found in tokens
        //if you need more char escapes refere to http://www.december.com/html/spec/esccodes.html
        
        NSString *current = [NSString stringWithFormat:@"&%@=%@",key,strValue];
        [post appendString: current];
    }
    
    //we build the request
    request = [NSMutableURLRequest requestWithURL:
               [NSURL URLWithString:@"https://www.mercadopago.com/mlv/orderpreference"]];
    
    NSData *postData = [post dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES];
    [request setValue:[NSString stringWithFormat:@"%d", [postData length]] forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postData];
    
    //we send the request
    NSData *urlData = [NSURLConnection sendSynchronousRequest:request returningResponse:&theResponse error:&errorReturned];
    
    //and we recieve the post answer
    NSString* url = [[NSString alloc] initWithData:urlData
                                          encoding:NSUTF8StringEncoding];
    if ([url hasPrefix:@"http"]) {
        return url;
    }else{
        return @"Error contacting MercadoPago";
    }
}

@end