I'm here to share some insights about this invoice template question.
Yes, you're right. You can only set one default message in the Message to customer field of your invoice templates. Regarding the footer details, this option cannot be moved as footers are meant to appear at the bottom margin of a document.
If you need different messages for your customers, you can leave that field blank on all templates, and just input the message as you create the invoices. See this:
Please know that you can share your suggestion within the program through sending a product feedback. Follow the steps below in a web browser:
Click the Gear icon and choose Feedback.
Enter your suggestion for our engineers on the Feedback box.
Once done, press Next to send it.
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