The billing page features information on your billing cycle and most recent charges, your payment methods, and a list of your previous transactions. If you click on a transaction ID, you will be taken to a more detailed view of that invoice.
If you miss a payment, your paid access will downgrade to the sandbox tier. If you would like to continue to access a paid tier, please re-upgrade via the subscriptions page
You will notice a "Charge date" field within the "Billing" page. This is the date during which your use case and account was approved by the Twitter team. If you upgrade, you will pay a prorated fee to get you through your Charge date. From then until you downgrade, you will be charged the subscription fee on your charge date.