A cost you paid, recovered exactly once.
Record what you spent against the customer or project it was for. Mark it rebillable and it is ready to add straight onto their next invoice — and once it is on one, it is claimed, so nobody can put the same cost on a second invoice by mistake.
What a firm actually does with this
Log it against the project
Materials, a subcontractor, a licence bought for one client — recorded where the work happened, not in a spreadsheet somebody has to remember to check.
Rebill it, or don’t
Some costs are yours to absorb; others are the customer’s to pay. The choice is per expense, not an all-or-nothing setting.
Onto the invoice, once
Add it to the next invoice with the amount already right — no retyping the figure from a receipt a second time.
Recurring costs, handled the same way
A cost that repeats — a monthly licence you pass on, for example — can be set to log itself on the same schedule as a subscription’s invoices, so it is never the one recurring line somebody has to remember by hand.