From your Dashboard go to Settings > Emails & Texts.

Locate Appointment Follow-Up tab under Email templates.

When you scroll down there will be a section with all the wildcards that can be used for these templates.

However there is a list of wildcards that DO NOT WORK with Appointment Follow-Up Email templates:

{{invoice.venmo_username}}

{{invoice.custom_payment_link}}

{{appointment.sales_tax_percentage}}

{{appointment.hashed_customer_items[:vat_number]}}

{{booking.first_name}}

{{booking.price}}

{{appointment.customer_notes}}

{{appointment.notes}}

{{appointment.work_items_}}

{{appointment.number}}

{{assignment.eta_sentence}}

{{booking.full_name}}

{{booking.my_company_phone_number}}

{{booking.address_alt}}