In Odoo, the default functionality of the POS module does not provide a direct option to create a single invoice for multiple POS orders. However, there are a couple of possible approaches to achieve this:

1. Use the Sales module: Instead of creating invoices directly from the POS module, you can leverage the Sales module to create a single invoice for multiple POS orders. Here's how you can do it:

   a. Create a Sales Order: Convert each POS order into a sales order individually. You can do this by navigating to Sales -> Orders and creating a new order for each POS order. Associate the relevant products, quantities, and customer information.

   b. Group Sales Orders: Once all the relevant sales orders are created, you can select and group them together using the "Merge" or "Group" functionality available in the Sales module. This will combine the individual orders into a single consolidated order.

   c. Create Invoice: From the consolidated sales order, you can generate an invoice by clicking on the "Create Invoice" button. This will create a single invoice for all the grouped sales orders, allowing you to bill the customer for multiple POS orders.

2. Custom Development: If the above approach does not meet your requirements, you can consider custom development to enhance the functionality of the POS module. This may involve creating a custom module or extending the existing POS module to support creating a single invoice for multiple POS orders. Custom development would require technical expertise or the assistance of an Odoo developer.