Chargebee being an advanced billing system charges you for the period ahead. So the 1st invoice will not move into a pending state.
From the 2nd invoice on, Chargebee puts the invoice in the pending state which gives you the ability to add charges that occurred during the previous billing period.
Pending invoices are generated only when you have the previous term’s unpaid consumption charges. When the 1st invoice is generated it can move into any of the below three statuses.
Paid - When payment was made successful
Payment Due - Charge has been attempted but failed.
Posted - When you've enabled Payment Terms (Net D) for your recurring invoices.
If you want to add any usage-based charges, you can do it when the subscription renews and the pending invoices get generated.
Visit our Help Docs to know more about how Metered Billing works. You can test this feature either by using the Time Machine or modifying the subscription’s renewal date (change next billing date to “Now”)
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