Sorry if this has already been answered, but I could not find it anywhere.
My company is based in Austin, TX, US, and is an LLC.
Do I have to pay sales tax on open invoices? I.e., Invoices for taxable sales that have been sent out, but not paid-in-full yet. This is a bit of a time sensitive question, since my sales taxes are due. ;)
Generally sales tax is something that the buyer pays, and the seller collects and remits to the agency. So you're not the one paying the tax, you're collecting it on behalf of the government (since Americans didn't want big government, they made every seller part of it...).
If the buyer hasn't yet paid - there's nothing for you to collect and remit. Accounting method (cash vs accrual) may be important here though, so be careful.
This, of course, is not a tax or legal advice, you should get a proper legal consultation from a Texas licensed attorney on any legal matter.