Input Variables & Tax Codes are core parts of the invoicing configuration within Zero Friction.
You can find these settings via Configuration → Invoicing → Input variables and Configuration → Invoicing → Tax codes.
Input variables are values that can change over time and are used in rate formulas.
Tax codes determine which VAT rate is applied to invoice lines, depending on the date and customer type.
Together, these configurations ensure correct price calculations and correct tax application on invoices.
Input variables
What does this part show?
The Input Variables page shows an overview of all input variables used in rate formulas within invoicing.
For each input variable you will see:
Name of the variable
Description of what the variable represents
Time-based values, including start and (optional) end dates
Each input variable can contain multiple values, with each value valid for a specific period. The system automatically uses the value applicable to the invoice period.
Layout
General information
Name
Unique identifier of the input variable (for example,EnergyPrice,NetworkFee).Description
Functional explanation of the meaning and application of the variable.
Values
Numerical values that are time-dependent
Start date and optional end date
Overlapping periods are not allowed
Translations
Input variables support translations
The variable must be saved first before translations can be added
A tooltip explicitly indicates this requirement
Actions
Users with appropriate rights can:
create input variables
add, change or end values
Remove input variables unless they are used in active rates or billing
Behaviors & Logic
Input variables are used within rate formulas, for example:
Unit Price = Energy Price × 1.1 + Network Fee
The system:
determines the invoice period
selects the value valid in that period for each input variable
replaces the variables in the rate formula
calculates the final rate
If an input variable does not have a value that covers the entire invoice period, billing will stop with an error message indicating which variable is missing.
Changes to input variables:
influence future invoices
have no retroactive effect on invoices already generated
Tax codes
What does this part show?
The Tax Codes page shows all tax codes available for invoicing.
For each tax code you will see:
Name of the tax code
One or more VAT rates
Validity periods per VAT rate
The combination of tax code and invoice date determines which VAT percentage is applied to invoice lines.
Layout
General information
Name
Recognizable name of the tax code (for example Standard VAT, Reduced rate).
VAT rates
Percentage (e.g. 21%, 9%)
Validity period per rate
Exactly one VAT rate per date may be active per tax code
Overlapping or missing periods are not allowed
Actions
Users with administrative rights can:
create tax codes
add or change VAT rates
Delete tax codes, if not in use
A tax code cannot be deleted if it:
is set as the default tax code for advance payments
is linked to one or more invoice items
Behaviors & Logic
When calculating VAT on invoices:
the system determines the tax code based on the invoice item
selects the VAT rate valid on the invoice date
calculates the VAT amount based on the net amount
adds the VAT amount to the total amount of the invoice line
When a VAT rate changes within a single invoice period, the system automatically splits the invoice line so that each part uses the correct VAT rate.
Changes to tax codes:
only apply to new invoices
have no influence on invoices already sent
Problem | Solution |
Input variable has no value for period | Add a value that covers the entire period |
Invoice line is split | Check if a VAT rate changes within the period |
Tax code cannot be deleted | Check if this is still in use or set as default |
Rate calculation fails | Check error message for missing input variables |
Error message “input variables missing” | Add missing values for the period |
Overlapping VAT rates | Adjust dates so there is no overlap |
No tax code available | Check if at least one rate is active |
Change has no effect | Check the start date of the new value or rate |
Why can't I delete a tax code?
Because it is still in use or has been set as the default for advances.
Can I set overlapping VAT rates?
No, each date can only have one active rate.
What happens if I change an input variable?
New invoices will use the new value; existing invoices will not be recalculated.
What if a variable is missing during invoicing?
Billing stops with an error message.
Do input variables support multiple languages?
Yes, via translations after the first save.
How do I choose the correct tax code?
Based on local legislation and customer type (organization or residential).
What happens if there is a VAT change in the middle of the period?
The invoice line is automatically split.
Input Variable (Cost Component) – Time-dependent value used in rate formulas
Tax Code – Collection of VAT rates with validity periods
VAT Rate – Percentage applied to an invoice line
Time-sliced – Data with different values per period
Invoice Item – Product or service on an invoice
Rate Formula – Mathematical calculation for pricing
Advance invoice – Invoice before final settlement
VAT – Value Added Tax