Problem tracking exceptions in Google Analytics 4

I'm trying to use Google Analytics 4 to track payment errors with Stripe.

I'm using Drupal 8; here is the relevant JS:

// Helper to handle the Stripe responses with errors.
var stripeErrorHandler = function (result) {
  if (result.error) {
    // Inform the user if there was an error.
    // Display the message error in the payment form.
    Drupal.commerceStripe.displayError(result.error.message);
    window.dataLayer = window.dataLayer || [];

    function gtag(){dataLayer.push(arguments);}
    gtag('event', 'exception', {
      'description': result.error.message,
      'fatal': false
    });

    // Allow the customer to re-submit the form.
    $form.find(':input.button--primary').prop('disabled', false);
  }

The gtag() function is taken from the Google developer documentation for pushing exceptions in GA4.

I turned on debug mode in Analytics, went to the checkout page, and input an invalid expiration date.

In the Chrome dev console, I can see that the exception is logged:

Processing GTAG command: ["event", "exception", {description: "Your card has expired.", fatal: false}]

However, the exception does not actually get logged in Analytics. What more do I need to do to get the exception logged?