Hello there, Casey. I'll share some insights about customizing your invoice within your QuickBooks Online (QBO) account to help you get back on track.

The T isn't visible on your invoices because you're using the Modernized template. To make it appear, you need to switch to the Other template.

To get started, you'll need to customize your invoice template. For detailed instructions, please refer to the following link: Customize invoice in QBO.

Once ready, you can create and update invoices with the new template. Here's how:

1. Create or edit an invoice.
2. Click Manage.
3. Under the Design tab, select the invoice template you customized earlier under the Other templates section.

You can click Print and download to save the PDF and review it before sending.

For future guidance, you can look up this article about recording customer payments in QBO: Record invoice payments in QuickBooks Online. You can either record payment for a single invoice or partial payments.

If you have any more questions regarding customizing sales forms within the program, drop a comment below to receive a prompt response. I'm always here to help.