Once the user applies the vouchers during the registration, the code is attributed to the user and can be found with hover the mouse over the username, clicking the username details or in the separate column in the exported file of users.
If you decide later that you do not want to use all of the vouchers, you can simply delete them using the Archive/Prolong feature and the respective number of licences will be returned into Credit available.
How will English test users apply the activation voucher?
There are two ways how can users unlock all English proficiency levels with the activation voucher.
a) They can use the classic registration flow where they create the account with an e-mail and password and in the next step, they will be asked to submit the voucher.
b) Another option is the easier one. Users can use the dedicated page https://app.tracktest.eu/voucher (works also with the custom URLs) where they add username/e-mail and voucher. This page works for the both first-time registration and login of the existing user.
Here is a short video tutorial: