To switch a tier to yearly billing or ask for a volume discount, see "The Core, Pro and Ultra tiers".
Your invoices
All your invoices (credit top-ups and tier subscriptions) are available in your billing portal: Billing → Invoices and payments. There you can download the PDFs, update your payment method and review your payment history.
VAT
Desirely prices are shown excl. VAT. The applicable VAT depends on your situation (individual or company, country, intra-EU VAT number). Fill in your billing details, including your VAT number if you have one, from the Invoices and payments portal: they appear on your invoices.