In Odoo POS the Return button doesn’t directly handle exchanges. It only allows you to return products from a validated order (by entering the original receipt/Order Ref). If you want to exchange, the standard flow is:

1. Use Return to process the product being given back.
2. Validate that return (creates a refund).
3. Start a new order in POS and add the replacement product.
4. Collect the payment difference if applicable.

So exchanges are managed as Return + New Sale. There isn’t a one-click exchange function by default in Odoo POS. If you need a single-step exchange button, it requires customization or a marketplace module.

Hi,

In Odoo 18.3 POS, the refund flow is intentionally sequential: you must end the refund before starting a new order. That’s why the system blocks adding products to a refund ticket—refunds and sales are handled as two separate transactions.

To improve this, you can install a module like POS Product Exchange, which enables true in-POS exchanges: you can return items, add new ones, and complete the difference payment—all in the same session.

You can refer this module - https://apps.odoo.com/apps/modules/17.0/product_exchange_pos_sys

Hope it helps