You can easily get an invoice or all your invoices directly in your WebSelf account.
To do this, go to the avatar tab located on the right side of the Dashboard and click on My Profile.
Click on the Billing and Payments sub-tab; here are your options:
BILLING HISTORY
In this section, you can view information about your invoices: Payment date, Description, Site, Amount, Status, and Bill (available for download in PDF format).
To get an invoice, click on the PDF file icon on the right; the invoice will be saved in the "Downloads" folder.