Hi @PMWilson, thanks for your question.
The hyperlink on the invoice that you are referring to is live and will update to reflect the current amount that is on the invoice.
Keep in mind that after you edit an invoice, you can also resend it to your customer with the updated information by clicking Save and send after those edits have been made.
This article includes some instructions and a video.
If you have any more questions, please don't hesitate to reach back out!