This article is about the invoices Zenamu issues to your studio for your Zenamu plan. It isn't about receipts or invoices you issue to your clients — those are in Orders (see Receipt vs invoice: which document type to issue to your clients).
You can find your Zenamu invoices on the Plan page, in the Zenamu subscription payments table:
Open the Plan page. On a computer, click the Plan button in the top bar next to your profile menu. On a phone, open the main menu and tap Plan. Only users with Administrator permissions (the super admin role) can open this page. It isn't in Settings.
In the Zenamu subscription payments table, find the payment. Use the Year filter for older payments.
Click the eye icon in the Details column, then click View invoice details. Or click the file icon in the Document column directly.
The table is shown once you've made at least one payment to Zenamu. For a payment by bank transfer that hasn't been invoiced yet, the link reads View payment request instead of View invoice details.