StoreProduct IsInUserCollection is always false - windows-store-apps

Question

We have a UWP product in the Microsoft Store. The product has a number of subscription add-ons. Users make in-app purchases of subscription add-ons.
EDIT Our code is cobbled from Microsoft Docs Enable subscription add-ons for your app
StorePurchaseResult result = await product.RequestPurchaseAsync();
if (result.Status == StorePurchaseStatus.Succeeded)
The result returns StorePurchaseStatus.Succeeded. Microsoft has taken the user's money for the subscription add-on. All good so far.
We qet a product list like this
string[] productKinds = { "Durable" };
List<String> filterList = new List<string>(productKinds);
StoreProductQueryResult queryResult = await storeContext.GetAssociatedStoreProductsAsync(filterList);
productList = queryResult.Products.Values.ToList();
Then iterate through
foreach (StoreProduct storeProduct in products)
{
if (storeProduct.IsInUserCollection)
...
}
but storeProduct.IsInUserCollection always returns false. Microsoft has accepted payment for the add-on but not added it to the user's collection of products, so we cannot verify they have paid for the add-on.
Where did we go wrong?
EDIT 2 Following a suggestion from #lukeja I ran this method
async Task CheckSubsAsync()
{
StoreContext context = context = StoreContext.GetDefault();
StoreAppLicense appLicense = await context.GetAppLicenseAsync();
foreach (var addOnLicense in appLicense.AddOnLicenses)
{
StoreLicense license = addOnLicense.Value;
Debug.WriteLine($"license.SkuStoreId {license.SkuStoreId}");
}
}
This outputs only a single add-on. The free add-on. We have 16 add-ons only one of which is free.
Why aren't any of our paid add-on subscriptions returned?
EDIT 3 appLicense.AddOnLicenses only includes add-on licenses for the current user, not all add-ons for the app. The code sample provided by #lukeja works as expected when run within the context of the user who paid the subscription.

Answer 1

I'm not sure why you're using that method. The way I'm currently doing it in my app and the way that Microsoft's documentation suggests is like this...
private async Task<bool> CheckIfUserHasSubscriptionAsync()
{
StoreAppLicense appLicense = await context.GetAppLicenseAsync();
// Check if the customer has the rights to the subscription.
foreach (var addOnLicense in appLicense.AddOnLicenses)
{
StoreLicense license = addOnLicense.Value;
if (license.IsActive)
{
// The expiration date is available in the license.ExpirationDate property.
return true;
}
}
// The customer does not have a license to the subscription.
return false;
}