Critical error or warning?
Short answer
Not every warning means the invoice is wrong. In general: * critical error (Error, Fatal) means that the invoice is a problem that needs to be corrected, * warning means that the system has found something you should check, but the invoice may not be automatically incorrect. Simple: Critical error = invoice probably cannot be sent. Warning = check the invoice, but it may not be a problem.
Critical error
In particular, the missing mandatory data, incorrect XML structure, breach of the calculation rule, unauthorised code or missing identifier.
Warning
Warning may indicate an unadvised value, a missing optional or an indication that may be required by a particular partner.
Meaning depends on the instrument
Markings Error, Fatal and Warning are not universally defined by law. The documentation of the validator used should be based on that used.
Internal rules
It is recommended to determine which warnings are only registered, which are repaired before dispatch and who decides on the exemption.
Conclusion
Not legal advice. Machine-translated answer, not yet manually reviewed. For the exact wording, see the Slovak original.