Up to 2 attachments (including images) can be used with a maximum of 524.3 kB each and 1.0 MB total.
Sorry that the updated Web App Tester supporting the newest WebView wasn't ready when you went to download it. It's been republished to the Appstore and should be available for you to download now.
I have encountered the same issue. Tried 3 different devices. 2 Fire TV Sloanes and one Fire Tv stick
1 Person is following this question.
Can firetv webapp attach handler for back and menu button? How is youtube app doing this?
Is DRM playback supported thru the use of ExoPlayer integrated with Cordova?
Fire TV Web App redirection to external payment page
Fire TV Webview exoplayer crash
How do you do a background video for HTML5 FireTV app?