Expert articles on EU billing, DATEV, XRechnung, VAT OSS quarterly filing and SaaS invoicing.https://kontier.eu/enhttps://kontier.eu/en/blog/idempotent-usage-event-processing/https://kontier.eu/en/blog/idempotent-usage-event-processing/What a usage event's idempotency key should be made of, how long to keep it, and what to do with events that arrive after the billing period has closed.Fri, 09 Oct 2026 19:50:09 GMTUsage-based billingIdempotencyUsage eventshttps://kontier.eu/en/blog/eu-vat-oss-automation-billing-system/https://kontier.eu/en/blog/eu-vat-oss-automation-billing-system/How the One Stop Shop works for digital services, and which fields your billing system should store per invoice line so the quarterly return builds itself.Fri, 09 Oct 2026 19:50:08 GMTEU VATOSSData modelhttps://kontier.eu/en/blog/product-catalog-versioning-saas/https://kontier.eu/en/blog/product-catalog-versioning-saas/Why a plan shouldn't just have a price: plan versions, sales and contract periods, pricing snapshots on the invoice line, and meter versions.Fri, 09 Oct 2026 19:50:08 GMTProduct cataloguePrice changesUsage-based billinghttps://kontier.eu/en/blog/datev-export-saas-billing-without-excel/https://kontier.eu/en/blog/datev-export-saas-billing-without-excel/What goes into the DATEV posting batch, how postings link to invoices, and which three balances must agree at month end, with a worked Stripe clearing example.Fri, 09 Oct 2026 19:50:08 GMTDATEVaccountingmonth-end closehttps://kontier.eu/en/blog/billing-software-for-european-saas/https://kontier.eu/en/blog/billing-software-for-european-saas/What to demand from billing software for the EU market, weighted must and should, and how to test each requirement yourself in a vendor demo.Fri, 09 Oct 2026 19:50:08 GMTbilling softwarevendor selectionEU VAThttps://kontier.eu/en/blog/seat-based-billing-software/https://kontier.eu/en/blog/seat-based-billing-software/20 seats added on 16 April, 10 removed in May, 30 more on an annual contract: three seat cases worked through, with the rules your contract should state.Fri, 09 Oct 2026 19:50:07 GMTseat-based billingprorationSaaS contractshttps://kontier.eu/en/blog/api-based-billing-platform-europe/https://kontier.eu/en/blog/api-based-billing-platform-europe/Sandbox, idempotency keys, RFC 9457 error format, webhook outages, data export: a concrete two-week test plan for choosing a billing API.Fri, 09 Oct 2026 19:50:07 GMTBilling APIVendor selectionIdempotencyhttps://kontier.eu/en/blog/automate-vies-vat-id-checks/https://kontier.eu/en/blog/automate-vies-vat-id-checks/A validation workflow for EU VAT IDs in SaaS billing: normalisation, statuses for outages, retry rules, the German BZSt option and proof that matches each invoice.Fri, 09 Oct 2026 19:50:07 GMTVAT IDVIESReverse chargehttps://kontier.eu/en/blog/saas-price-changes-without-deployment/https://kontier.eu/en/blog/saas-price-changes-without-deployment/From €99 to €119 per seat: what a new price means for monthly customers, annual contracts, grandfathered accounts and open quotes, and what breaks on the day.Fri, 09 Oct 2026 19:50:07 GMTprice changesproduct catalogueSaaS billinghttps://kontier.eu/en/blog/create-reverse-charge-invoice/https://kontier.eu/en/blog/create-reverse-charge-invoice/Mandatory details and their typical mistakes, the exact wording, an annotated sample invoice, VAT category AE in the XML and the EC Sales List check.Fri, 09 Oct 2026 19:50:07 GMTReverse chargeInvoicingEC Sales Listhttps://kontier.eu/en/blog/validate-xrechnung-en-16931/https://kontier.eu/en/blog/validate-xrechnung-en-16931/Three validation layers, one validator, five recurring rule failures: how SaaS teams check XRechnung before sending instead of after the customer complains.Fri, 09 Oct 2026 19:50:07 GMTXRechnungEN 16931e-invoicinghttps://kontier.eu/en/blog/e-invoicing-software-for-saas/https://kontier.eu/en/blog/e-invoicing-software-for-saas/Receiving since 2025, issuing from 2027 or 2028: which capabilities e-invoicing software for SaaS needs, when, and what to test in the vendor demo.Fri, 09 Oct 2026 19:50:06 GMTe-invoicingXRechnungZUGFeRDsoftware selectionhttps://kontier.eu/en/blog/avoid-eu-tax-billing-mistakes/https://kontier.eu/en/blog/avoid-eu-tax-billing-mistakes/A failure catalogue for EU VAT in billing: how each error shows up, where it comes from, how to correct it and which query catches it early next time.Fri, 14 Aug 2026 09:17:26 GMTEU VATInvoice correctionsSaaS billinghttps://kontier.eu/en/blog/integrate-webhooks-into-billing/https://kontier.eu/en/blog/integrate-webhooks-into-billing/Signature checks per Standard Webhooks, deduplication by message ID, ordering by object version, and a reconciliation job for missed events.Sat, 08 Aug 2026 13:53:20 GMTWebhooksPayment statusBilling APIhttps://kontier.eu/en/blog/billing-api-europe-b2b-billing/https://kontier.eu/en/blog/billing-api-europe-b2b-billing/Tax profile, invoice snapshot, credit note, selling entity: the data objects where generic billing APIs break down in European B2B.Sat, 08 Aug 2026 13:53:19 GMTBilling APIB2B billingReverse chargehttps://kontier.eu/en/blog/gobd-compliant-invoicing-software-saas/https://kontier.eu/en/blog/gobd-compliant-invoicing-software-saas/Germany's GoBD principles applied to a SaaS billing stack: locking, versioned master data, deletion dates from year end, and process documentation that keeps up with releases.Sat, 08 Aug 2026 13:53:18 GMTGoBDrecord retentionGermanyhttps://kontier.eu/en/blog/automate-ifrs-15-saas-billing/https://kontier.eu/en/blog/automate-ifrs-15-saas-billing/One SaaS contract with a licence, a migration fee and API usage, run through the five IFRS 15 steps: allocation, January revenue and a mid-year upgrade.Sat, 08 Aug 2026 13:53:17 GMTIFRS 15revenue recognitionusage billinghttps://kontier.eu/en/blog/tiered-pricing-saas-billing/https://kontier.eu/en/blog/tiered-pricing-saas-billing/One price table, two invoice totals: volume and graduated tiers worked through, with the boundary cliff, the counting scope and the rounding rule.Sat, 08 Aug 2026 13:53:16 GMTtiered pricingusage billingpricing modelshttps://kontier.eu/en/blog/automate-overage-billing/https://kontier.eu/en/blog/automate-overage-billing/A plan with 5,000 included documents, worked through: what happens to the allowance on a mid-month upgrade and when the overage gets invoiced.Sat, 08 Aug 2026 13:53:14 GMToverage billingusage billingSEPAhttps://kontier.eu/en/blog/evaluate-usage-based-billing-software/https://kontier.eu/en/blog/evaluate-usage-based-billing-software/A scorecard for usage-based billing: idempotency, late events, pricing models, traceability and EU tax, tested on your own data rather than vendor slides.Sat, 08 Aug 2026 13:53:13 GMTusage-based billingvendor selectionmeteringhttps://kontier.eu/en/blog/peppol-integration-billing-system/https://kontier.eu/en/blog/peppol-integration-billing-system/Peppol is a delivery network, not a format. When SaaS vendors need it, how access points and participant IDs work, and what your billing system has to store.Sat, 08 Aug 2026 13:53:12 GMTPeppole-invoicingXRechnunghttps://kontier.eu/en/blog/xrechnung-saas-invoices-implementation/https://kontier.eu/en/blog/xrechnung-saas-invoices-implementation/Seats, prorated add-on seats and API usage as an XRechnung: the fields your billing data model has to supply, and where the Leitweg-ID comes from.Sat, 08 Aug 2026 13:53:11 GMTXRechnunge-invoicingdata modelLeitweg-IDhttps://kontier.eu/en/blog/dunning-software-subscriptions/https://kontier.eu/en/blog/dunning-software-subscriptions/When a business customer is in default, what you can then charge, a dunning sequence day by day, and six cases where the automation has to stop.Sat, 08 Aug 2026 13:53:10 GMTDunningReceivablesB2Bhttps://kontier.eu/en/blog/sepa-direct-debit-saas/https://kontier.eu/en/blog/sepa-direct-debit-saas/What matters before, during and after collection: creditor ID, mandate evidence, refund windows, the B2B scheme, pre-notification and return codes.Sat, 08 Aug 2026 13:53:09 GMTSEPA Direct DebitPaymentsB2Bhttps://kontier.eu/en/blog/reverse-charge-software-billing/https://kontier.eu/en/blog/reverse-charge-software-billing/A decision table, a state model for VAT numbers, one decision record per invoice line, and what must happen on status changes and credit notes.Sat, 08 Aug 2026 13:53:08 GMTReverse chargeVAT IDBilling architecturehttps://kontier.eu/en/blog/eu-tax-logic-saas-implementation/https://kontier.eu/en/blog/eu-tax-logic-saas-implementation/Five tax questions, one fixed order and a stored decision object per invoice line: how to build EU tax logic you can test and explain line by line.Sat, 08 Aug 2026 13:49:27 GMTEU VATArchitectureSaaS billinghttps://kontier.eu/en/blog/subscription-billing-eu-market-saas-billing-for-europe/https://kontier.eu/en/blog/subscription-billing-eu-market-saas-billing-for-europe/An architecture for EU subscription billing: data model, immutable events, the tax decision at invoice creation, and returned debits that actually reach the product.Sun, 05 Jul 2026 18:19:06 GMTsubscription billingarchitectureSEPAhttps://kontier.eu/en/blog/automate-eu-vat-oss-without-special-case-logic/https://kontier.eu/en/blog/automate-eu-vat-oss-without-special-case-logic/What to check between quarter end and filing the OSS return, and how credit notes and late VAT IDs should land in quarters you've already closed.Sun, 05 Jul 2026 18:19:06 GMTOSSQuarter closeEU VAT