Additional services are additional to rental charges (e.g., final cleaning). They can be created/edited as templates in the pricing model and per booking:
A) price model
Templates for additional services in the pricing model:

B) booking
Services can be created for each booking under Services using New service or adding a preset service from the pricing model:

With Add new service a service is added as a flat price without a calculation.
Price calculations are available using Calculate new service. The number of persons (adults, children, adults + children) and the days/nights of the booking can be included in the calculation. Below is an example showing the calculation method (total = A * B * C * D):

In the Pricing, the number of persons (adults, children, adults + children) can optionally be stored with an offset. As an example a service from the third person:

