There can be several reasons a pack is unable to download.

1. Poor Internet Connection

Firstly check you are on a good WiFi connection, some of the packs are quite big and might take a while to come down. It might also be a good idea to download one pack at a time if your connection is not very fast.

2. Insufficient Storage Space

Please check you have sufficient space on your device for the packs to download. You can find your free storage space by going to Settings -> General -> Storage & iCloud Usage

3. You may have downloaded them

Some people have been expecting to see all the filters appear in the filter section of the app at once. They are in fact only displayed one pack at a time. So you need to go to the pack picker (where you purchased the pack) and tap the pack you wish to select. The current pack is indicated by a tick in the bottom right corner.

In order to prevent the row of buttons at the bottom of the app getting too long we have kept the filters in their respective "packs". To switch to the pack you purchased you need to go to the pack picker where you purchased the pack - then tap on it to make it active. The packs you have purchased will not have a price on them any more.

If the pack you have purchased has a price on it you may need to restore your purchases by pressing the "restore" button in the top right. Please make sure your device is signed in with the same Apple ID that you used to purchase the pack.

more information can be found from apple here:

support.apple.com/en-gb/HT204530