Does POE out work properly when usino 12v power supply?

Hi I'm thinking about buying 2 hap ax³, which have POE in-out on ether1. The goal would be power the second router through the first one. The problem is that where the first router is located only 12v (3.5Amps).

Here is stated that:

"If a device supports powering other devices using PoE-out, then it is recommended to use at least 18V as the input voltage"

What issues could I be encountering?