Hey there, @quickjelly. 

Thanks for following up with us. I'm happy to provide additional insight into applying credits to invoices. 

At this time, the only option to apply credits to an invoice is by checking the Apply existing credits box at the bottom of the invoice. However, I can see how having the ability to apply a specific amount would be beneficial for you and your business. I've submitted a feedback request to our product development team, so this can be considered in a future update. 

In the meantime, feel free to check out our Blog Site to keep up with our latest happenings and updates.  

Please let me know if there's anything else that I can do for you. You can reach out to the Community at any time. Enjoy your weekend!