The ability to send Invoices directly from QuickBooks Online via text message isn't available at this time. I'll pass along this idea to our Product Development team for possible implementation in future releases of QuickBooks Online.
In the meantime, I recommend checking out our Apps Marketplace to see if there is a third-party integration that allows this. You can also check out our blog for updates on new releases for QuickBooks Online.
Please let me know if there's anything else I can do to be of assistance. Wishing you and your business continued success in all that you do.
One option on the marketplace is SnapDesk.app. They have a solid 2-way sync with Quickbooks online that makes it easy to text invoices directly to your customers phones so they can pay from a mobile device.