For what reason would you send an invoice @spahrsautographs if it's not to adjust the amount due? Expanding on what ebooksdiva said with my standard response about sending invoices:
There's no reason to send an invoice unless you have to make an adjustment, for example combined shipping costs or adding another shipping method the buyer requested.
eBay sends out payment reminders to buyers automatically. Sending invoices is a duplication of efforts and clogs the buyer's inbox.
Sending an invoice locks in the shipping cost. That could have a big financial impact on someone that uses calculated shipping. The shipping price gets locked in based on the buyer's default location, but if they change the address at checkout to have that item shipped to Mom across the country, that shipping cost can change by leaps and bounds and seller is out the $$.
Finally, sending an invoice resets the clock on when an order can be cancelled for non-payment when sellers handle UPIs manually. The automated system will cancel based on the seller's settings regardless of sending an invoice, but when you use the manual process and an invoice is sent it resets the clock, giving the buyer an additional 4 days before the system will let the seller cancel.
