Your K-12 school district has purchased access to Cengage for its students, but when you create an account and sign in at the main Cengage home page, you are told your trial access will expire and asked for payment.
Cause
You used the higher education portal to create an account instead of the K-12 portal. Accounts created through the K-12 portal at nglsync.cengage.com/register are not asked for payment.
Resolution
Create a K-12 account and enroll in your course at nglsync.cengage.com/register. Always sign in at nglsync.cengage.com.