As a material supplier, we often invoice months before we ship materials. For example, I have 3 unpaid invoices dated from January, but I didn't ship materials until May. I know some people calculate monthly notice deadlines from invoice dates, but I don't believe that is legally acceptable in my situation. Can you provide further info on the state statute and what is legally acceptable? Also, am I required to send a copy of my unpaid invoice with my Texas notices? Where in the statute does it mandate this?