Generate image assets from layers - not working with multiple files and droplet

For the record, the dependency on the action can be removed with the following edit to the previous script:

for (var i = 0; i < app.documents.length; i++) {
    app.activeDocument = app.documents[i];
        var idAdobeScriptAutomationScripts = stringIDToTypeID( "AdobeScriptAutomation Scripts" );
        var desc99 = new ActionDescriptor();
        var idjsNm = charIDToTypeID( "jsNm" );
        desc99.putString( idjsNm, """Image Assets""" );
        executeAction( idAdobeScriptAutomationScripts, desc99, DialogModes.NO );
    // Adjust value as required for quantity of open docs
    $.sleep(1000);
};
alert('Ensure that all assets have been saved before closing the active documents!');

Try the following script. Open all images into Photoshop with appropriate layer names to trigger Generate Image Assets. Two things to note:

1. You need to create an action set and action with a single step to "Generate Image Assets" and use that name in the script (or name your action set and action as per the original script).

2. You may need to increase the sleep value to give the script time to loop through all open files.

for (var i = 0; i < app.documents.length; i++) {
    app.activeDocument = app.documents[i];
    // Change the action and set as required
    app.doAction("Generate On", "Generate Image Assets.atn");
    // Adjust value as required for quantity of open docs
    $.sleep(1000);
};
alert('Ensure that all assets have been saved before closing the active documents!');

Once you have confirmed that all assets have been generated, you can close down all open documents in one go, with or without saving.

With Photoshop 2019, I get an error that the script is not available when running the inserted menu command for Generate: Image Assets from a Batch or the Image Processor or Image Processor Pro scripts.

I wanted to test what happens when an action plays another action...

When you have a problem with an action its always best if you post your actions so we can analyze what the action is doing.