Providing the best experience with the product is what we aim for, @Brnstrmr.

There's no specific time frame on when the feature to merge invoices or any other types of transactions will be available in QuickBooks Online (QBO). I'd recommend sending this request straight to our product engineers through feedback. Sharing features and options that you would like implemented is how our engineers look for new product updates. Here's how: 

1. Go to the Gear icon at the top.
2. Select Feedback.
3. Enter your comments or product suggestions.
4. Then select Next to submit feedback.

You'll want to check for a third-party application that can help you with this one. You can check out the apps that are compatible with QuickBooks at this link: https://quickbooks.intuit.com/app/apps/home/. We can also do it in QBO by following the steps below:

1. Go to Apps on the left side menu.
2. Search for the app in the Find apps to streamline your work field.
3. Look for the app that supports the Batch Invoicing feature.

Any questions about integrating the app into your Online account are best handled by the third-party app provider. In the meantime, just delete the second invoice so it will not become a duplicate. Let me show you how:

1. Go to the Sales menu.
2. Click the Invoices tab.
3. Look for the invoice and click on it.
4. Select Edit invoice in the lower-right hand corner.
5. Add the products or service items from the second invoice.
6. Press Save and send.

For more tips and other resources, you may visit our page in managing your business in QuickBooks: QBO Self-help articles.

I'll be right here to continue helping if you have any other concerns or questions about QuickBooks. Assistance is just a post away. Take care always.