In order to take Credit Card payments for any reservations, you'll need to fully set up your Stripe account. During the setup process, you'll need to enter Personally Identifiable Information (PII) to verify your business info and banking info with Stripe.
To access Stripe Setup:
In the main Settings Cogwheel, navigate to Account -> Stripe Setup.
If you've gone through the setup process in the past, the next step will ask for a phone number to send a verification code to. If it's your first time going into Stripe setup, it'll have a button to start the account creation process.
In addition, if there are any outstanding issues with your Stripe account, you'll see a banner similar to this across the top of your Staylist window when logging in: