I need to setup just one invoice for one client with multiple matters for a law firm. i want this to be automated be in using qbo or any third party apps. please help

It sounds like you need to find a third party law software that integrates with QuickBooks Online, you will have to research apps/software yourself, I would just look for reviews and demos for law firms.  Then if you find one that integrates with QuickBooks Online, you can connect it through your QuickBooks online > Apps Section

There is usually a settings page in your third party software on how things are synced with QuickBooks Online. 

I agree with KimAnnVA. I highly encourage you to explore the Apps menu within QuickBooks Online. This menu is a treasure trove of integration options that can significantly enhance your invoicing process and overall workflow.

Here's how:

1. Go to Apps and select Find apps.
2. Use the search field to use keywords about your needs.
3. Click the related applications to see their details.

Please note that while we are unable to recommend specific third-party applications, this policy helps ensure fairness and allows you to explore all available options to find the best fit for your needs.

Moreover, you can consider using recurring invoices to streamline the billing process, improve cash flow management, and reduce administrative burdens, making them an essential tool for businesses that require regular invoicing.

Additionally, you can refer to this article about personalizing your sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online
 

Let us know if you have other concern with your invoices in QBO. We're here to help you in any way we can.