Custom field in sale invoice

I am trying to create a custom field in sales invoices, a thank you for your business line. Both options available seem not to work appropriately. I am sure, this is easily manageable.

You need to explain what you did. Show a screen shot of the Edit screen for the custom field. And what options are you claiming do not work?

Thanks, I figured it out myself. So easy, actually:
I wanted to have a “Thank you” note below invoice lines.

  1. I created a custom field without a label and without description.
  2. In form defaults I entered the text, like “Thank you for your business.”

Voila, simple as that.