Online Business Account customers
If you are an OBA customer, your manifest paperwork is considered proof of postage by Royal Mail. In addition to the copy you hand over with your post, you can also print out and keep additional copies for your records.
For more information on manifesting your orders, please see this guide: How to manifest your orders.
Personal customers
If you are a personal customer, there is a checkbox within your label settings which you can use to generate a proof of postage document along with your label.
Once you have changed this setting, you can generate a proof of postage document for orders that have already been despatched by selecting the order, then clicking the 'Re generate paperwork' button.