How do I change the card I pay with?

If you installed nouz from the Shopify App Store, your plan is paid with whatever pays your Shopify bill. So you change it in your Shopify admin, under Settings and then Billing. nouz never sees your card. That is also why no card goes into nouz when you start the trial.

If nouz bills you directly, open Settings, then Billing in nouz. Find the row called Payment method. It shows your card, for example Visa ending 1234, expires 08/27. Click Replace card, or Add card if there is none. The card form opens inside nouz. Your details go straight to Stripe, the payment company, and we never see or store a card number.

A new card is used from the next invoice. If a payment has already failed, add a working card and the payment can go through straight away. Only the owner can change the card. The Billing details row below it holds your company name, address and VAT ID for your invoices.