How to add an expense reimbursement in a payroll check
In File, Preferences, Payroll, Earning/Deductions Codes, add a Non Taxable Income Account called Expense Reimbursement.
In the Employee's record, Earnings Tab, add the Earnings Type you just set up in the prior step. After processing payroll, unmark this earnings code so you don't have to deal with it every payroll. After updating any employees record, remember to reset the record on the second page when you process payroll.