In order to assign fee type to grade, please follow the steps mentioned below,:
Go to Fee Management > Fee Types
Click on three dotted icon
Click on "Assign Fee Type to Grade(s) or Student(s)".
Click on Grades.
Search for Grade name and select the required record.
Click on Assign button.
Fee is assigned to the selected Grade. (click on upward arrow)
You can also refer to article How to assign fee type to student for details.
Note: When a fee type is assigned to a grade, then for all the enrolled students in the grade, if any student has an open & unpaid invoice, then assigned fee type is added to the invoice. Otherwise, a new invoice will be generated.