Yes I got this partial working with the List Expression in the Toolbox plugin.
I have a weird problem. As you suggested I built the created a list by creating a Thing every time an item was created.
Then I added a Save button. When the Save button was clicked I used the List Expression to create the list & set this list as the JSON array in the POST request.
The problem I have is that when I set the Data Source for the List expression I can see in the debugger that the list expression evaluates to an empty string
In the image there are 2 elements in the list but I can’t see any data for these elements. However I know that these elements were created. Everytime I try to set the Data Source it returns an empty string.
Any ideas what the problem could be. Could the database be corrupted?