This error is most common when a student is using MyLabsPlus, but purchased a regular MyMathLab code.
We do ask students to purchase by ISBN only to ensure they're buying the code needed for their class.
This is the product needed for most MyLabsPlus courses: https://forresterbooks.com/products/978-0558928889-mymathlab-in-mylabsplus-student-code-e-delivery
While access code purchases are not returnable, we do offer exchanges.
The student will just be responsible for the difference in cost.