FastBill API Documentation

All documented changes to the FastBill API reference in reverse chronological order.

01.10.2026

Invoice Estimate Recurring Item

Added New fields DISCOUNT_PERCENT and DISCOUNT_AMOUNT at document and item level in invoice.create / update / estimate.create / recurring.create / update
Added New response fields DISCOUNT_BASE_AMOUNT, DISCOUNT_PERCENT, DISCOUNT_AMOUNT and DISCOUNT_TOTAL at document level plus DISCOUNT_BASE_AMOUNT, DISCOUNT_PERCENT and DISCOUNT_AMOUNT per item in invoice.get / estimate.get / recurring.get
Added New response fields DISCOUNT_BASE_AMOUNT, DISCOUNT_PERCENT and DISCOUNT_AMOUNT in item.get

22.09.2026

Invoice Estimate Recurring Revenue Expense

Added New fields BASE_CURRENCY_CODE and EXCHANGE_RATE in the response of invoice.get / estimate.get / recurring.get / revenue.get / expense.get
Added New filter and response field IS_GROSS in invoice.get / recurring.get
Changed Field DETAILS_URL in invoice.get is now also returned for drafts (previously only for invoices and credit notes)
Fixed Invoices created with gross values now return the correct document totals and item values in invoice.get / recurring.get

16.09.2026

Webhook

Changed Webhooks are now available in all plans (previously only in the Pro and Premium plans)

21.08.2026

Invoice

Added New field SUBTYPE in actions invoice.get / create / update
Added New field PREVIOUS_INVOICE_ID in actions invoice.get / create / update
Added New field NEXT_INVOICE_ID in the response of invoice.get

03.07.2026

Customer

Added New field GLN in actions customer.get / create / update

02.06.2026

Invoice

Changed VAT_CASE in invoice.create / update and recurring.create now only accepts defined VAT cases

08.05.2026

Invoice

Fixed Service period in invoice.create now defaults to invoice date when no period is specified

27.04.2026

Invoice

Changed VAT_CASE slugs in invoice.create / update and recurring.create now use external identifiers (e.g. small_business_regulation instead of small_business)

22.04.2026

Customer

Changed Field BANK_BIC in customer.create is no longer required

14.04.2026

Invoice

Added New fields CUSTOMER_ACCOUNTING_NOTE, CONTRACT_REFERENCE, CUSTOMER_ORDER_REFERENCE and ORDER_REFERENCE in invoice.get / create / update

27.11.2025

Customer

Changed Field COMMENT in customer.create / update, invoice.create / update, expense.create and revenue.create now has a maximum length of 1000 characters

18.11.2025

Invoice

Added Filter STATE in invoice.get now additionally supports values canceled and issued
Changed Status value created in invoice.get response has been renamed to issued

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