I applied for the DTV in the Netherlands. I got rejected because they were missing a document from the Muay Thai gym. But no one knows which document that is and the embassy can't clarify it more than:

a certificate issued to the school/gym from office of boxing sport board, sport authority of Thailand

Does anyone know what document they are talking about, what it looks like, or any information that can clear this up? All the official documents have been submitted but this one seems to be a mystery but they need it anyway.

Any clarification will be much appreciated.