Where I'll find the ultimate XML schemes; and Schematrony for Slovak e-invoice?
Short answer
Definite technical artifacts should be searched in official sources: Peppol BIS Billing for European rules, OpenPeppol for validation artefacts and official technical publications Financial Administration or Peppol Slovak authorities for Slovak specifics. An old copy is not enough for implementation XSD the project; To be monitored version, effective date and Slovak CIUS rules.
Technical structure
It controls elements, order and types of data.
Business rules
Checks totals, VAT logic and data relationships.
National additions
It specifies the European model for Slovak requirements.
Effective date
Implementation must know which version of the rules it used.
Conclusion
Definitely XSD a Schematrony to be taken from official sources in circulation; correct Slovak e-invoice not only must pass XML structure, but also Peppol and national business rules.
Financial Administration of the Slovak Republic, FAQ 9/VAT/2025/IM k e-invoice, July 2026 update
Not legal advice. Machine-translated answer, not yet manually reviewed. For the exact wording, see the Slovak original.