How to enable a user to select multiple values in an App

Hi all,

I have a scenario where the end user has a list of customer codes. Depending on their needs they might want to select a single customer code or a dozen for the robot to process. I have all of this set up nicely except for the method for the end user to initially provide input to the robot.
I have all these customer codes stored in the Data Service under an Entity.

I was hoping in the Apps I would be able to somehow use a Listbox where I could select multiple items, but sadly this isn’t the case. I can only select one at a time.

I have looked using the listbox events to do something, but there is only one event when an item is clicked on (i’d prefer a double click).
Even using that event, its hard to build a variable that contains the JSON Ienumerable I’d need to make for the process input because the function builder doesn’t seem to escape quotation marks correctly and I’d need something like
But I am unable to do this so far…

I’m generally looking for insight and ideas. I don’t have much experience in App Studio so hoping someone else with more experience might be able to drop a few ideas.

Thanks in advance.

Jon Smith