Hello there, @Denise3,

The option to send multiple forms to a single customer is only available for QuickBooks 2020. If you're using a later or lower versions, the checkbox for Combine forms to a recipient in one email will not be available for them.

See this article to learn more about this feature: Email sales forms in QuickBooks Desktop.

To complete your tasks, continue emailing the forms just like what Michelle_b suggested in her answer. You can also opt to upgrade your service to the latest version. See the current pricing and features for QuickBooks 2020: Choose your QuickBooks Desktop product.

If you have other questions about QuickBooks and its processes, let me know in the comment. I'll be more than happy to share and provide further assistance. Have a good one!