Status 408 means the SMP has no record of the buyer, so the invoice can't be delivered. Confirm the buyer's registration before you try again.

1. Verify the buyer's participant identifier format and value.

   Confirm with the buyer that their IČO is correct and that they've registered with a PEPPOL-accredited Access Point in Slovakia.

2. If the buyer confirms they're registered, check whether their endpoint is published in the Slovak SMP.

   Ask their Access Point to verify.

3. Don't resubmit until you've confirmed the buyer's registration is active.

   Resubmitting to an unregistered participant generates another 408.

   There's no confirmed fallback delivery method when a buyer isn't found on the Slovak PEPPOL network. Email distribution is listed as out of scope for this release.