Does vMix charge a subscription?

Purchasing vMix is a one-time transaction. There is no need to subscribe. When you buy a vMix Registration Key, it is valid indefinitely and does not expire.

Your purchase also includes one year of free version updates. For example, if you bought vMix in September, you would be able to update it to any newly released versions for free until September of the following year! If you want to update to a newly released version after the one-year free update period has ended, you can pay a very small upgrade fee. This purchase also includes another year of free version updates. Otherwise, you are not required to purchase an upgrade and can use vMix up to the version you have activated indefinitely.