Categorization of expense reimbursements

I recently had to travel to a customer site, for which travel expenses are to be reimbursed to me by the customer. I’ve already filed the expense as a purchase but in which category and sub-category should I categorize it in the invoice, given that it’s not really a sale but a reimbursable expense?

If you are claiming your mileage expenses as well then this reimbursement is part of your sale