To create a fee that can be added to either your quotes, order, or invoices, navigate to My Account > Fees.
Then select "Create Fee".
Here you have the option of making it either a flat-fee or a percentage of the total the customer will pay. Don't forget to hit save after you've configured your fee.
Note: For Lightspeed R-Series you can link this to one of your products. Lightspeed X-Series (Vend) and Shopify users don't have this option.
Once the fee's been created you can add this to either your quotes, orders, or invoices. To do so navigate to the document where you'd like to add the fee and create the document as usual, if you need a refresher check out this article on how to create an invoice. Once your document looks good navigate to the subtotal section and click on "Fee".
Click "Add a fee".
From there select the fee you'd like to add to the document, then click save.
You'll see that the fee, in our example the shipping fee, has been added to the subtotal section.