S Corp 1120S Form K1 - non-passive unreimbursed business expenses

You cannot deduct unreimbursed expenses from an S Corp- all deductions must be through the S Corp and reported on the 1120S.  You can establish a an accountable plan to reimburse employees of the S Corp.  

https://www.investopedia.com/terms/a/accountableplan.asp#:~:text=An%20accountable%20plan%20is 

here is more info about an accountable lan. rules must be followed otherwise the iRS will treat it as a non-accountable plan

there are two options for the employer. reporting should be done regularly ie not waiting until year-end to do the reporting

1) give the employee and advance and the within the required time limit required documentation is submitted and the employee reimburses the company for any excess

2) the employee submits a periodic expense report and then is reimbursed either directly or through payroll with it clearly indicated.