Therapeutic practice seeks online appointment booking system

I am looking for an online appointment booking system for my therapeutic practice (counseling/coaching/seminars).

I have the following requirements for the software:

• Customers make their own bookings online
• When booking, they agree to the terms and conditions
• Appointments are binding and can only be canceled up to a specified time before the appointment
• Reminder via text message or email
• Option to sign up for newsletters
• Option to request customer feedback
• Different appointment types
• Phone
• Practice
• Conversation with an individual
• Conversation with a family
• Later also seminars
• Customer database can be imported into other systems, e.g., email marketing software
• Possible future option to also sell products and pay online
• Windows compatible
• High security standard, data protection (e.g., encryption, certified data center in Germany), as sensitive client data is handled

Two software workstations are planned for the time being.