To link a negotiating body to a pay element:
Go to Setup and click Settings.
Select Module Settings and then Payroll Settings.
Click Pay Element.
Search for the pay element and click on it.
Tick the Addition Deduction Grade Required box.
Click Add Grades.
Select the payroll, negotiating body and upper grades and pay scales.
Click Save.
When adding this pay element to an employee as an addition to basic pay you will be able to choose a payscale within the lower to upper payscales you've selected.