Hi, non-persistent entities are not working for the Email module.
Since non-persistent entities per default are send to the client, and the server doesn’t keep track of them, the server won’t even remember the object once send to the client.
The email module retrieves it’s data from database, based on a passed guid, and for that guid, no object is found in the database.
As stated in an earlier question you could use a non persistent object but you would need to pass that object to the point where the Java action is actually sending the mail. You can not retrieve it because they only live client side.
Can you share a screenshot with the error?
Please have a look at below image