The old web API (rbxassetid://http://www.roblox.com/Thumbs/Asset.ashx?width=WIDTH&height=HEIGHT&assetId=ASSET_ID) no longer works for gamepasses because they have their own asset ID system.
Example
Image using the web API and new gamepass ID:
And here’s the actual gamepass:
Having API access to asset images is really useful - it makes it so that we do not need to upload duplicate images, and do not need to manually add & change images for assets like gamepasses in a shop GUI.