If you don't want to alert your existing customers (with appointments in your current system) when adding those appointments into the Unwritten app follow the steps below.
Step 1 - Make sure your SMS appointment notifications is not turned on yet.
Step 2 - Add the customer to the Unwritten app without using their email, and only use their name, mobile number (and address if you have it).
Step 3 - Add the customers appointment(s). The customer will not get an email confirmation of their appointment as they have no email, and they will not receive the SMS as it is not turned on.
Step 4 - Go back and add their email address (so they will receive reminders and bills in future)
Step 4 - Continue with your other customers and appointments until complete
Step 5 - Turn SMS reminders back on (if you want to use them).