Pop-in, iframe and mini-site URL integrations also allow you to use parameters (GET or JavaScript) to determine :

lang : the widget language can be defined if you want to offer it in a specific language: German (de), English (en), Spanish (es), French (fr), Italian (it), Japanese (ja), Dutch (nl), Portuguese (pt).
service : the service ID (or its external ID) to be selected for scheduling appointments
serviceGroup : the service group ID (or its external ID) to be selected for scheduling
resource :the ID of the resource to be selected for the reservation
resourceGroups: the ID of the resource group to be selected for the reservation
staff: the ID of the team member (or their external ID) to be pre-selected for this appointment booking
staffGroup: the ID of the group of team members to be selected for the appointment
gid: the GoogleAnalytics tracking code, if any
cs: deactivation of the branch selector

schedulingMode :
service: select service only
service-staff: choose the service and then the team member
staff-service: choose the member of staff then the service
date: date to be preselected (date=YYYY-MM-DD)
minAppointmentDate: minimum delay before an appointment can be made (eg: fixed date minAppointmentDate=YYYY-MM-DD or minAppointmentDate=days-3; same syntax as for the Settings API JSON properties)
maxAppointmentDate: maximum period of time within which an appointment can be made (eg: fixed date minAppointmentDate=YYYY-MM-DD or maxAppointmentDate=months-2; same syntax as for the Settings API JSON properties)
form field ID: the value of a field (visible or hidden) to be pre-filled (see the article Pre-filling contact data in the appointment booking module).
Example: item reference consulted when making an appointment
personal data: you can also pre-fill personal data such as first name, surname, email address, telephone number, etc. (please consult the corresponding documentation)
tagId: ID of the tag to be associated with the contact in CRM
source: customisation of the source of the appointment booking (acquisition channel), for example :
source=fb to indicate appointments booked from Facebook
source=site to indicate appointments booked from your website
these indications will be visible in the Appointments by source reports

Setting up URL / GET links for scheduling appointments

GET and JS parameters for the appointment scheduling widget