If you've upgraded to a paid plan, you can find your invoices on the page below:
Settings > Plan > Payment History
For Plus Users:
Underneath where your plan details are listed, please select, “Payment History.”
Please put additional information, such as your company's address or tax number, in the Note field.
For Business Users
Next to where it says your Plan description, click “Payment Detail.” Then, once you have been redirected to the ‘Payment’ tab on your Nulab Account page, you can download any existing invoices. To add notes, such as your company's address or tax number, click “Change” next to where it says “Billing.”