C5 is the Access Point of Finančná správa for the Tax Data Document Slovakia (TDD SK). It is not the C2 to C3 chain. Only a domestic transaction (Slovakia to Slovakia) sends a TDD to C5. Status back from C5 uses MLS, not Invoice Response. The country context is in the overview.

C5 rejects the message if any of these five is missing:

1. The document type is TDD. Another type is rejected at AS4 level.
2. The receiver is exactly the C5 identifier from the SMP ([0242:001180]).
3. The message is structurally valid under the Peppol AS4 profile.
4. The message is signed with a valid Peppol certificate.
5. The message is encrypted to the C5 certificate.

The AS4 acknowledgement follows immediately. Validation and further processing are asynchronous.

The service provider's SMP registration must support the MLS document type, otherwise C5 cannot return a status. Failed MLS deliveries are retried and then given up.

Every TDD is validated against the TaxData XSD and Schematron. On failure the document is not stored and a negative MLS follows with the errors. A TDD has no attachments. The message stays under 10 MB.

If a transport condition fails, there is no AS4 acknowledgement. Fix the cause and send again.

The integration environment is only reachable from IP addresses in EU member states. The endpoint still comes from the SMP, including in this table: the host is the target the SMP points to, not an address you fix in code.

C5 submission is separate from C2 to C3. A failure, timeout or outage at C5 must not block invoice delivery. Do not wait for the AS4 acknowledgement or the MLS from C5 before you treat the buyer as reached. Retries use a growing pause, and each AS4 message keeps its own Message ID.