Once you have placed a bid that includes your rates but without the expenses (mileage, tolls, parking) and the requestor accepts it. It is the terms that the requestor and you have agreed to. You will not be able to add expenses to your invoice after placing a bid without expenses.
It is important to make sure what rates and expenses you want to include in your bid before placing it so that the requestor will know what terms you are offering for your services.
NOTE: If an assignment shows that specific expenses can be reimbursed as part of the terms, you will be allowed to include them in your bid. However, some assignments do not have any reimbursable expenses, and they cannot be included in your bid. Please review the terms of an assignment before bidding.