Hi there, @vytronaccounting. I can see that it's not pleasant for you to add a non-sales product to your sales. Let me share some information about adding the prepaid freight payment to the invoices.
In accounting, what the customer pays you for the shipping is your income. On the other side of the process, what you pay for actual shipping to the customer is an expense.
With this, you can create a service item called "pre-paid shipping" and select an income account for it. To avoid posting it to the general Income account, you can create a new account and name it as "Pre-paid shipping" or whichever you prefer.
This is how the Invoice looks like if you are going to add the prepaid freight:
I would also suggest contacting your accountant to give you more options with Pre-paid Shipping.
I have here an article you can check in the future about managing your business' records: Understand reports.
Please don't hesitate if you have other questions or concerns. Take care and more power to your business!