ga - free_to_paid

// Fire this event when a user successfully upgrades from the free plan to a paid plan.

<script>
window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
 'event': 'free_to_paid',
 'user_plan': 'pro',  //Variable value based on the plan the user selected. E.g. "basic", "pro", etc.
 'payment_frequency': 'monthly',  //Variable value. E.g. "monthly" or "annually".
 'user_id': 'asdf1234'  //User ID from your website database.
 });
</script>