Absence applies to staff in all schools and pupil referral units (PRUs) but doesn't apply to centrally employed staff. It's required for teachers and teaching assistants in regular service working for schools through a contract, not an agency agreement.
To include absence in the SWC export, you need to set the SWC absence category against each applicable absence class in the system. To do this:
Go to Setup, then click Settings.
Click Module Settings then click HR.
Click Absence Class.
Click each applicable absence class.
Under SWC Code, select the relevant option.
Click Save.