The Bitstack card is a debit card. Each payment is debited directly from your cash account: you can only spend the funds available in your account.
The card is subject to the following limits:
Card payments: €5,000 per month
ATM withdrawals: €200 per week, for a total of €1,000 per month
You can check these limits at any time in the app, under Cash → your card → Limits.
Your card limits cannot be changed. Since the card works as an immediate debit, it is not possible to go into overdraft: any payment exceeding your available balance will be automatically declined.