JavaScript for Automation: import CSV and press ok for mapping popup

Automation OmniPlan Automation
1

I try to Open a CSV file (and then Export that one) using JavaScript for Automation (JXA).
Using OmniPlan v2.

When I manually open (import) a CSV file a popup appears to map the columns.
The mapping that is shown is fine, so all I have to do is press OK (or press Enter).

How do I achieve this using JavaScript for Automation?
When I try this the app.open() call is stuck until I manually press ok for the popup.

What I tried:

var systemEvents = Application('System Events')
var app = Application("OmniPlan")
app.open(Path("~/Documents/omniplan_import.csv"))
// popup appears: "Map Columns" ← how to select "OK"?
console.log("import completed") // only reaches this one after manually closing the popup
systemEvents.keyCode(36); // therefore sending Enter keycode has no effect
2

With the excellent help from Christian (thanks!), this is the workaround we came up with.
Make sure you have Script Editor enabled in System Preferences > Security & Privacy > Accessibility.

var systemEvents = Application('System Events')
var app = Application("OmniPlan")
try {
  // open the CSV (popup appears) and let this timeout after 1 second so we can send Enter
  app.open(Path("/Users/myname/Documents/omniplan_import.csv")), {timeout: 1})
} catch(error) {
  // send Enter (OK) to use the default values and close the popup
  systemEvents.keyCode(36);
}
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