Your VIP status is active for 30 days after a purchase. After that, the status expires and VIP bonuses become inactive (e.g., VIP buildings and decorations will remain at your estate but won't give bonuses). To reenable VIP and keep using the bonuses, you need to make a new payment for any amount.

If you make a payment while your VIP status is still active, it will get extended from the date of the latest payment.

Even if your status has expired, when you make the next purchase (even a couple of months later) you will start at the same VIP level that you had previously.