Hi deeztreez21,
Welcome to the QuickBooks Community! I'll share information about emailing an invoice.
QuickBooks has no indicator for an invoice being sent because the process happens so quickly. A successfully sent invoice has a Last delivery remark while an unsuccessfully sent one has a Delivery error remark.

If there's anything that I can help you with your invoice, feel free to reach back out. Take care and have a good day!