Decoding the phrase

I have no idea what the following phrase actually means: challenge coins custom so I'm not even going to try.   Sometimes these odd phrases turn up in the work I do for a company online, and because of the nature of the job, it's not always easy to figure out quite what the 'employer' is getting at.  Never mind, we know it's something to do with a challenge, with coins, and with custom. 

You could do quite a bit with that, I'm sure....write a short poem, even.

It's a bit of a challenge
to write a poem on coins
that's according to custom,
by which I mean the challenge
of using some normal form
of poem, as is the custom;
but in this instance the challenge
may be with fake coins
which may involve Customs
and their challenge of you.

There we go; no more obscure than the original phrase.   Not bad for a draft poem, though I'm sure it can be improved upon....