You need to disconnect and reconnect your Gmail address to update the modified email signature in QuickBooks Online, Kelly.
Before sending the transaction to your customers, ensure that the Gmail address you are utilizing matches the email information entered in your file.
To do this in your QBO account, open the specific sales invoice and select Review and Send. From the Email your Invoice page, refer to these steps:
- Click on the From ▼ dropdown and tap Remove Gmail address.
- Then, select Add Gmail address and enter your Gmail information.
- Review other details and click Send Invoice.

Once done, your updated email signature in Gmail settings will now appear in QBO when you send emails to your customers.
In addition, here's how you can review and keep track of customer-paid invoices in your file: Record invoice payments.
If there's anything else you need further assistance, feel free to let us know in this thread.