How do I activate trial software with a Teacher/Student code?

I downloaded the trial version of Acrobat Pro to test it out berfore purchase.  If I wish to activate it with the Teacher/Student code, how is this done?  On the program, when I click 'activate', my only options are the full price monthly omngoing payments.  I don't want to purchase this platform and be stuck with the monthly payment vs the one time Teacher/Student cost.  Thank you.