For all Walls.io self-service plans, downloadable invoices are automatically generated in your Walls.io account. You can find them by logging in with your account and clicking "Invoices" on the dashboard:
You will then see all of your invoices listed and ready to be downloaded:
Apart from that, you can download an invoice directly from your monthly payment confirmations:
In case you have further questions, don't hesitate to contact the support team via the chat or firstname.lastname@example.org!