Do I pay VAT, and where is my invoice?

No VAT is charged: the company that sells Panoramr is not registered for VAT, so the price you see is the price you pay. If that changes, VAT will be added to the price of payments made after the change.

Each payment has an invoice. Open the Vault (click Dashboard in the top bar, then the Vaults tab, then Open on the Vault) and look under Payments: each line has an Invoice link. A change that cost nothing has no invoice, and if somebody else paid for the Vault, the invoice is theirs.

Your latest payments, for plans and for Vaults, are also listed under Payments on the Plan & billing page, each with an Invoice link: click your name or picture at the top right, then My Account, then Plan & billing in the list at the left. VAT, invoices and refunds for a Vault has the rest.