When you use a boxed copy of FL Studio, there are a couple of situations where you will be asked to register your copy online. These include:
The registration process of your FL Studio boxed copy consists of two steps. If you have already registered your serial number online, you will just need to download and RUN a regcode (see the second step).
register the box serial number online:
download and run a regcode:
See the KB article Where can I get my registration code for instructions.
The FL studio Support Team.