If you exceed the monthly quota in your WeatherKit plan what happens when you make an API call (Swift SDK), does it just error out? Will Apple give you some grace period to upgrade your quota to a larger value before stopping you from being able to make queries?
As your usage approaches your monthly quota you will get notifications informing you of the percentage of quota that has been used. If you choose not to upgrade before the quota is exhausted, further requests to WeatherKit may be rejected with a Not Authorized error until you either upgrade or your quota resets at the end of the month.