You can change the device's quota in the User center or Android AirDroid Personal Me page (on your phone). The device's quota can remain until your Premium subscription is finished.
How to charge the increased device？
When you increase the device quota, it is equivalent to repurchasing an order.
If you pay with Google Play, when the remaining value of the old order is used up, you will need to pay the price for the new order after increasing the device, and the price of the recurring order will change accordingly.
If you pay via Stripe, you do not need to pay for the difference of the increased device immediately. Instead, it will be deducted along with the recurring subscription price on the 1st of next month.
If you use PayPal for payment, you need to pay for the difference of increased device immediately. On the 1st of next month, it will deduct the price of a new order.
How to return the money after reducing the device?
When you reduce the device quota, it is equivalent to repurchasing an order.
If you pay with Google Play, the order will take effect immediately when you reduce the device. You can remaining use the value of the old order until it is used up, then you'll need to pay the price for the new order after reducing the device, and the price of the recurring order will change accordingly.
If you pay via Stripe, when you reduce the device, the order will take effect immediately. The money of reducing the device will deduct the price of recurring payments for the next month.
If you use PayPal for payment, when you reduce the device, the new order will not be effective immediately, and the old order will still be used until the next month.
Note:
Premium users can connect up to 10 devices. If you want to connect more devices, please use AirDroid Business.