Hello,
On Anki’s main screen, go to AnkiHub and check if it says that media is “Idle” — this means the media download is complete on your computer. Media syncing can take a while, especially the first time — sometimes even hours — depending on your internet connection.
If it does say “Idle” and you’re still experiencing the issue, try resetting local changes by following this guide:
How to Reset Local Changes
It can take even longer for the media to be synced to AnkiWeb from your computer and then downloaded to your mobile device. You can click the Anki (not AnkiHub) sync button to check the current status of the media sync and see if it’s still in progress.
Let me know if you need help with anything else!