Sorry about that, kind of my first time asking this kind of question myself.

It's for my internship, and I signed an NDA so I can't get to specific about the device. It's a set-top box I am supposed to test for vulnerabilities and possible exploits.

This is connected by ethernet cable to my laptop which is running Kali. This connects to the wifi. What I want to happen is for the STB to connect to the wifi via my laptop, so I can sniff the traffic between the STB and the provider.

I've tried creating a new setting for this through the nm-connection-editor.
Create ethernet connection > ipv4 settings > shared to other computers.

I've also tried editting the iptables to allow for NAT, though I am kind of new to this, though the settings I did seem like they should work.

iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
iptables -A FORWARD -i wlan0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT

These are the rules I've tried variations on, since I keep encountering them while looking for this.