If you are being asked to start a plan, or the code is not accepted, it sounds like you may have accidentally signed up the 'regular' way (this is different to subscriptions provided by your university or company).
Fear not! Just follow these quick steps.
Delete your account via your account settings.
Follow the registration link provided by your school (it should take you to a 'group-register' page)
Enter your code and details!
If you need anything else or have any questions, then feel free to get in touch 😊