Sometimes the underlying bank denies verification on first attempt. Kindly try verifying their Chocolate card again as follows
In the Chocolate Finance app,
Ensure your Chocolate Visa debit card is not frozen
Ensure there is sufficient SGD 1 card balance in your Chocolate Visa debit card
Proceed to the HeyMax app,
You may click on "Try again to verify card"
If the issue with verifying your Chocolate Visa card persists, you may reach out to HeyMax support with Card linking support ticket.