Hello Chris
The error seems to indicate the API key has perhaps expired.
If you’re certain your players need to browse through your Asset Library then you can create a new API key for them that will not expire.
For normal play, the players don’t need the API key and they will access their own Assets Library (which for players is 100mb, enough for a lot of avatar and token images).
For a guide on the API key manager, please read this: The Forge API Key Manager
If you find that your players don’t actually need an API key, as soon as they remove the existing key, which has probably expired, the error will go away.
Hope this helps!