Downloading stopped at 0%

Here is my code:

```
SwiftyStoreKit.updatedDownloadsHandler = { downloads in

// contentURL is not nil if downloadState == .finished
let contentURLs = downloads.compactMap { $0.contentURL }
for download in downloads {
print("\(download.progress)")
}
if contentURLs.count == downloads.count {
downloads.forEach { [weak self] (download) in
self?.procesessDownload(downloadURL: download.contentURL, productId: download.contentIdentifier)
}
SwiftyStoreKit.finishTransaction(downloads[0].transaction)
}
}
```

I have 3 IAP items. The first one is ok. I can download after purchase. The other 2 are not working after purchase. It stopped at progress 0. Don't know the reason. How should I debug it? Thanks.