Finally I got the solution.
The tool description should be
Insert an object in database. Send with the different json just with the values of the
{{ $fromAI('full_name', `Name of the customer`, 'string') }},
{{ $fromAI('contact', `Customer's contact`, 'string') }},
{{ $fromAI('description', `Appointment description`, 'string') }},
{{ $fromAI('start_appointment_time', `Start time of the appointment (ISO datetime)`, 'string') }},
{{ $fromAI('end_appointment_time', `End time of the appointment (ISO datetime)`, 'string') }}
and the Fields should be like exact key values: full_name,contact,description,start_appointment_time,end_appointment_time
