There are two different ways you can add a surcharge to your client's sale. The first way will only work if you don't have the Advanced Discounting enabled, and the second way is what you do if you do have the Advanced Discounting enabled.
Product or Service as a Surcharge.
One way to add a surcharge or booking fee to a client's sale is to have a service or product called Surcharge and add it to POS and change the price of it on the fly.
Keep in mind though, that you can only change the price of items in POS on the fly if you don't have Advanced Discounting enabled. If you do have Advanced Discounting enabled, then follow the steps in the Discount Type as a Surcharge section of this article to see how to create and apply surcharges a different way.
To create a surcharge as a product or service simply go to Admin, then into either the Services or Products tab, choose or create a new Brand or Service Category for it to go under, then click New to create the actual service or product. Give it a name on the right side panel i.e "Surcharge", "Booking Fee" (whatever you like), keep the Retail Price as $0, (put 0 in Quantity if it's a product), then Save.
Now go to POS add the client to the sale, click Add Items, choose Products or Services (depending on what you created the surcharge as) and choose the "Surcharge" from the menus on the right side panel. Enter the surcharge amount in Final Price, and Save. The amount will be added to the clients sale.
Discount Type as a Surcharge.
The other way to do it is to set up a negative amount Discount Type, which instead of taking an amount off the sale, like a regular discount does, it will add an amount to the sale.
Firstly, you'll need to enable the Advanced Discounting by going to Settings, then into Cash Register Settings, tick Enabled Advanced Discounting, then click Save.
Now go to Admin, then into the Lists tab, drop down the Select Lists menu and choose Discount Types. Click New to create one on the right side panel. Give the discount type a name (i.e. "Surcharge") and keep the Percentage (%) ticked. Put the percentage amount in the Amount field with a - sign in front of the number (i.e. -2). Then click Save.
What this will do now when you add the surcharge to the clients services/products in POS is it will figure out what 2% (or whatever your percentage is) of the price is and then add that 2% onto the sale amount.
Go to POS, add the client to the sale, add their items (products and/or services), click the service listed in POS, on the right side panel choose the Surcharge discount type from the Discount Type field and Save.
The price will be adjusted accordingly. Do the same for each service and product listed in the sale for the total sale amount to update.
There you go, two different ways you can add a surcharge to your client's sale. To recap—the first way will only work if you don't have the Advanced Discounting enabled, and the second way is what you do if you do have the Advanced Discounting enabled.