Welcome to the Community. I'd be glad to assist you with any questions you may have with credit cards in QuickBooks Online.
You can only view the CVV Security Code upon setting up or updating the credit card information within the system. Once entered and accepted, this field will no longer be available for viewing.
If you want to ensure you have the correct security code, you can update this information. For additional reference, I'm adding some articles that I know will help you with the process:
Change your subscriptions's credit card information.
Please get in touch with me here should you have any additional questions or concerns about using credit cards in QuickBooks. Any additional information or screenshot will ensure a timely solution.