Your bank decides whether a card counts as debit or credit, and some banks class a card as credit even though it takes money straight from your account. Wio cards work this way, because the same card can spend from your balance or from a credit line.
When you pay, Ziina is told the card type, not which money it uses. So a card classed as credit is declined even when you're paying from your balance.
You can top up from your connected bank account instead, or use a debit card from another bank.