Unable to use https://products.groupdocs.app/comparison/total - Get "Undefined" alert when trying to compare

As the title says.
Unable to use the Compare files online | Free GroupDocs Apps service to test document. Even simple txt tests gives an alert of “Undefined”. Tested in Edge Chromium, Chrome, Firefox (all very recent versions). Also tried briefly on other system but inside same domain.

Getting:
angular.min.js:110 GET https://api.groupdocs.app/comparison/DocumentPages?SourceFileName=Test1.txt&FolderName=1796840c-474a-4bdb-b2a2-a027dede954f&TargetFileName=Test2.txt&UserEmail=none&PageNumber=1 500

Any suggestions on how to get it working? Something I’m missing?

@LeMaxim

This issue is reproduced at our end. We are now investigating it with ticket ID COMPARISONAPP-22. You’ll be notified in case of any update.