What do they mean by "A Promise"?

[romenren]

I understand that they surely don't mean me doing a pinky promise? It's stating I need documents showing I have health insurance or a "promise" of getting one, without the quotation marks. Do they mean a legal document? Something signed by a justice of the peace? Or do I just say "yeah, I'll definitely get one"? This is with the French Embassy in Wellington, New Zealand by the way