Welcome to the Sellers community as I see this is your first post.
Help me understand what your trying to do. You posted this in the Invoice section but are trying to print out your Gross sales Report. The Gross Sales report would show all sales not just invoice sales. I can not find what the Gross Sales Report is that your trying to print either. The images at the bottom of this reply show a list of the Reports on the Square Dashboard and none are a Gross Sales Report. I just tried to print out my Sales Summary report as a PDF and it did show the date.
The other thing I am confused on is the "Gross Sales Report". For these Reports I use a Computer and the Square Dashboard. Signin @ https://squareup.com/login Then Choose Reports and the Report you would like to print. If you are reading this on a Computer you could also jus follow the link : https://squareup.com/dashboard/sales/reports/sales-summary
When I went through the Reports it did have the Gross Sales, Net Sales..... ETC with a Date on top.
Are you using the Reports page from a Tablet or Phone trying to print these reports or through a computer and the Square Dash Board? Any help on your process, where you are trying to get the report "Gross Sales Report" and what device or devices you have tried would be helpful to answer your question. As you see below are a List of Report types from the Square Dashboard and none of them are called "Gross Sales Report", which is a source of confusion to answer your question. The sales summary Link above would give you a Gross sales summary for a selected Time Period and shows the date on the print out at least it did for the PDF version.
