The version of VPN that comes with Total Security has a limit of 200 MB of daily traffic. It also only connects to the closest, optimal server without your choice to connect to multiple servers worldwide as with the Premium.
The Premium version has unlimited VPN traffic. What you're using is like an introduction, a taste of how it works to see if it's something you would like to upgrade to, the Premium VPN. Some people are fine with 200 MB per day and only use it as needed.
More about it can be found here. The What is the difference between Bitdefender VPN and the Premium VPN version? in the article pretty much says what I mentioned.
See also from the above article:
How many devices does my Premium VPN subscription cover?
Regardless of the subscription type, Premium VPN can be used on maximum 10 devices at once.
If your Bitdefender security solution includes a Premium VPN subscription (e.g. Bitdefender Premium Security), then the VPN will inherit the device limit in that bundle (10, 15, etc.). It can protect the same number of devices as your Bitdefender security solution subscription, but no more than 10 devices connected at a time.
However, if your Bitdefender security solution does not include a Premium VPN subscription (such as Bitdefender Family Pack that covers up to 15 devices) when you purchase a Premium VPN subscription it will cover only 10 devices, not 15.
edit: depending on where you purchased your subscription from, on the main BD webpage, it is shown as 200 MB on its bullet points.
All Bitdefender Home Product User Guides:https://www.bitdefender.com/consumer/support/user-guides/