No tracking number on receipt. Please help

I recently sent very important documents using Canada Post (within montreal). I left the letter with them, paid the cost, they gave me the receipt but when i checked the receipt days later, it did not have a tracking number on it. I looked up their website and it said: « The tracking number won’t appear on your receipt if you used one of our prepaid products, but didn’t mail your package at the time of purchase. » What does that mean? Did they mail my package the same day or not? My receipt say i paid for postage on demand. I dont even know what postage on demand means with Canada post. The documents are headed to a government office with tight security so they cant even tell me if they’ve received my documents. Please help