If your Dialog is failing in PVA and the error message does not provide enough details, you can use Save snapshot feature to get the conversational diagnostics data in Test bot window in Authoring Canvas (provided you can reproduce the issue in Test).
In your Test bot window, go to the Menu on the right to find Save snapshot option:
Selecting Save snapshot option allows you to download bot content and conversational diagnostics for this session:
Bot content and conversational diagnostics will be saved into a DSAT.zip archive:
You can find conversational diagnostics in dialog.json file in DSAT.zip archive:
