Nested completion block not being called - ios

Question

I've got a nested completion block set to initialize an SKProduct. If I put a breakpoint right before the completion block, the inside block executes OK (I can poll for _product) but the completion block never fires.
If I call completion() immediately within this block it executes, but not if I call it within the completion block of the nested block.
- (void)initializeProduct:(NSString*)bundleId completion:(void(^)(BOOL finished, NSError* error))completion
{
// completion(YES, nil); If I call completion here, it executes
NSSet* dataSet;
dataSet = [[NSSet alloc] initWithArray:#[bundleId]];
[IAPShare sharedHelper].iap.production = NO;
if(![IAPShare sharedHelper].iap) {
NSSet* dataSet = [[NSSet alloc] initWithObjects:bundleId, nil];
[IAPShare sharedHelper].iap = [[IAPHelper alloc] initWithProductIdentifiers:dataSet];
[IAPShare sharedHelper].iap.products = #[bundleId];
}
[[IAPShare sharedHelper].iap requestProductsWithCompletion:^(SKProductsRequest* request,SKProductsResponse* response)
{
if(response > 0 ) {
_product = [[IAPShare sharedHelper].iap.products objectAtIndex:0]; // We get this far
// ^ breakpoint on this line shows _product is now an SKProduct
completion(YES, nil); // but this never fires
}
else
{
completion(YES, error);
// ^ yes, error is defined in my code, I'm being lazy
}
}];
}
I'm calling it in a method like this with another completion block (and it never enters the block):
- (void)priceForBundleId:(NSString *)bundleId completion:(void(^)(NSString* price))completion
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NO), ^{
[self initializeProduct:bundleId completion:^(BOOL finished, NSError *error) {
// Breakpoint placed here never catches
if (!error)
{
NSString* price = [RSStore priceAsStringForLocale:_product.priceLocale price:_product.price];
[defaults setValue:price forKey:#"bigBoxPrice"];
completion(price);
}
else
{
completion(nil);
}
}];
});
}