Víkingur is €24.99 a month, or €249.99 a year — paying yearly saves €24.89, a little under a month.
After the seven free days, the card you signed up with is charged and nothing else changes — the trial was already the full app.
Payment is handled by Paddle, the merchant of record. Paddle's checkout shows the exact price before you pay, handles VAT, and keeps your invoices.