The problem appears to be that a custom JavaScript action has been added, but the default functionality has not been removed. The default functionality is to throw an exception saying “JavaScript action was not implemented”.
The solution is to remove the exception from the action, and return a genuine value.
There is a good tutorial on how to do this in the Mendix documentation:
https://docs.mendix.com/howto/extensibility/write-javascript-actions
Hope this helps.