Hi there, Squeegee. There's no other way to add a tags or placeholders in the subject line, such as the invoice date.

I encourage you to share your thoughts directly with our Product Development Team through the Feedback feature in QuickBooks Online.

Here's how:

1. Click the Gear icon () in the upper-right corner.
2. Select Feedback.
3. Describe your request, such as: "Please add more dynamic placeholders, like [Invoice Date], to email subject lines for improved customization."
4. Click Submit.

If you need assistance or have additional questions, please don’t hesitate to reach out.