If you're getting a card error, make sure your card has enough funds and that you've entered the card number, expiry date, and CVV code correctly.
If you're not in the US, check with your bank that your card is enabled for international and online purchases.
If it's still not working, contact our support team at hello@simplified.com and we'll be happy to help. Send us a screenshot of the error, if possible, so we can better help you.