Wow, I was already imagining a type of ticket printed on some kind of wax paper where one could easily write permanently onto it. Disappointing to hear it was a typo.
It refers to exactly what they describe: A blank, open-ended ticket you can fill in by hand.
It's translucent slab of pale honey-scented wax whose faint, imprinted digits will distort if you press them too firmly. Also keep away from even moderate heat.
It's a decorated envelope, you write the destination on a clean sheet of paper then wax seal it with the company-issued signet ring.
I didn't know wax was used as a medium anywhere today. Isn't it heavy and hard to write on?
There is no wax. It was a typo.
That is certainly not what it describes.
The literal next sentence is 'His son could write the destination on them and fly for free'. That was added to be a description of what a 'wax ticket' is