zyBooks are steeply discounted for students, so most financial aid students initially subscribe directly using a credit card at zybooks.com, then "reimburse themselves" when their aid is disbursed several weeks into the term.
In rare hardship cases, we may defer payment for a few weeks. Email support@zybooks.com to request a deferment.
Or, you might check whether your bookstore sells zyBooks prepaid access keys, in which case you might use your school financial aid account to purchase a key from the bookstore. Info about prepaid access keys. Info for bookstore representatives. But note that most financial aid students pay directly at zybooks.com, which may have a lower price, enable future discounts, and save time too.
By the way, the first chapter is free, so you can immediately start reading and doing activities even before paying or requesting deferment. After you subscribe, you will appear on that zyBook's roster, and any activities you've already completed become visible to your instructor.