Under Setup | Settings | Payroll | Incomes:

Set up an income, with a type as a reimbursement.

Under Setup | Settings | Payroll | Linked Accounts | Incomes:

Set an account for Simply Accounting to record that reimbursement's amounts to.

Under the Payroll, Employee record, in the Income tab:

Enable the income type for that reimbursement.

More details are in the online help, search it for 'Reimbursement'

There is no easy way to record GST included in items that are being reimbursed.  If this is necessary, use one, generic type of GST taxable reimbursement, and record a two-line payable invoice to 'charge back' the amount reimbursed to the Reimbursement G/L account.   (the balance of the account should be zero if all reimbursements are recorded, and paid)

I hope that helps, please post back.

I presume everything is unchecked for this income type ?

I presume everything is unchecked for this income type ?

Affirmative.  Payroll Reimbursement should be un-checked for all deduction and tax types.