If you upgrade from the Developer plan to another monthly plan in the middle of the month, you will be charged the full monthly subscription fee upfront and receive the full verification allocation. Any verification sent in the current calendar month will count towards your first month's allocation of verifications. At the end of your first month, your plan will continue to renew at the start of each subsequent month for the full charge and allocation amount.
If you upgrade from the Developer plan to an annual plan in the middle of the month, you'll be charged upfront for 12 months' worth of subscription fees and receive the full monthly volume allocation. The current month will count as the first month of your subscription.
*Please note that verification volumes are applied based on calendar months and subscriptions renew on the first of each month at 12:00AM UTC.