To download an invoice for your purchase, you can log into your Todoist account at todoist.com, click the gear icon at the top and go to Todoist Settings > Payments.
Here you'll be able to enter the data you want to see on your invoice (your company name, address, VAT ID etc.) and download the invoice.
Please note that this option is only available for payments made directly through our site using a credit/debit card or PayPal. If you've paid through Apple's App Store or Google Play Store, an invoice can only be issued by the appropriate vendor (Apple or Google).