How to record reimbursement to be billed back to clients

This may shed light here How to archive Reimbursement in ERPnext?

edit: Apparently how and where reimbursable amounts can be recorded, as an asset or expense, accounts receivable etc, depends on accounting practice and laws in your locale.

Hence best to seek a qualified accountant who is legally responsible for their ‘solution’ - ERPNext is no more that the means to this end.