I have just googled : Combine postage with Simply Delivery and have come with below :
Combined Postage with Simple Delivery:
- Manual Invoice: If a buyer purchases multiple items, they can request a combined total from the seller.
- Seller Action: The seller can then send the buyer an invoice with the new, combined postage cost.
- Check Combined Invoices: Ensure that "Allow combined payments and postage" is enabled in your Postage Preferences.
- Void and Re-Purchase: If the buyer has paid for multiple items with Simple Delivery labels, you can void the labels and purchase a new one based on the combined package size/weight.
- Refund the Difference: If the new postage cost is less than the combined cost of the individual labels, you can refund the difference to the buyer.
