DataUnlocker charges you only for the traffic which was proxied through DataUnlocker's servers. By design, only blocked traffic is proxied, hence you are only charged for requests which were "unblocked".
DataUnlocker uses a pay-as-you-go prepaid billing model, meaning that you need to purchase the traffic first in order to use it for the proxy. Initially, you have 512 MB of traffic for all properties you create. You can use it for testing and verifying that DataUnlocker will work flawlessly with your web application.
Your properties are billed for each byte of traffic which goes through DataUnlocker's proxy. DataUnlocker counts both incoming (upload) and outgoing (download) traffic to its proxy services against your prepaid traffic. To be exact, DataUnlocker sums up a reverse proxy request size (which can also include additional headers and hence be a few bytes more than the original request) with the DataUnlocker's proxy response size (the response your website's users get from DataUnlocker). The size of a single proxied request is a total number of bytes it takes, which includes both headers and its body.
You can view the current prepaid traffic spending trend on the Property Billing page. The remaining prepaid traffic is displayed either on the chart or in the Usage Summary table. When the prepaid traffic reaches 0, DataUnlocker proxy will stop working and you will get an email notification. The proxy will be resumed immediately (with a maximum of 15 seconds delay) once you purchase some traffic.
DataUnlocker will also send you email notifications if the prepaid traffic of your property is getting low or runs out. You can configure the threshold at which the first email will be sent:
DataUnlocker also allows you transfer prepaid traffic from one property to another without limitations. You can transfer purchased traffic only, as well as previously transferred traffic. Thus, you can always move the traffic you have purchased between any properties you have access to.