Age Verification Ordering From Krale-Schietsport

I am thinking about ordering a 12 ft.lb HW-97 from Krale. It says on the page:

There is a restriction on this product.

This article is only for sale to people aged 18 and older; upon purchase of the article you need to establish your identity by providing a copy of your valid proof of identity. You can email this to us or send it by post.

Does anyone know what needs to be emailed to them as valid proof of identity?
 
Placed orders on a Sunday eve, rifles showed up on Wednesday (California). This was two separate orders about a month apart. Same fast shipping both times. Now the first one, the stupid UPS driver delivered it to the wrong address, so I didn't actually get it until the following Monday. Luckily no harm. The second order I had held at a UPS distribution center to be safe. It was available for pick up that Wednesday at 8AM. Pretty amazing.