How to test the «Card Register» feature using a sandbox account?

iyzico offers a secure card storage service for your customers to experience one-click payment.

When I click the «BUY» button inside the «Card Register» block in the «App Store» section of my merchant dashboard, the system responds: «An exception occured!» (with a misspelling).
So how to test the «Card Register» feature?

iyzico.com/en/solutions/iyzi-credit-card-storage/

iyzi Credit Card Storage Service allows customer’s credit card information to be securely stored in a fully PCI DSS compliant environment.
Users will not require to re-enter credit card information each time when shopping on your website. Our platform will recognize the user and store credit card information to allow an easy and quick checkout process.
Our service supports retail companies own POS system which will allow the users to still be able to use their coupons, instalments and other payment alternatives.
iyzi Credit Card Storage will shorten your acquisition funnels, make online shopping faster and easier, create easier and more user friendly checkout process and result in a revenue and conversion rate increase.

I have got an answer from the iyzico’s support:

I activated cardRegister for your account.
You can register the cards.