@BDF4 

Hello, as per the Tether compatibility list, the WR845N V4 should be compatible with the Tether app. Be sure you are running the latest firmware on the WR845N as well as for the Tether app.

If that has been confirmed, please follow this article to confirm all the basic settings:
https://www.tp-link.com/support/faq/2809/

If the Tether app still cannot find the router, please tell us the below information, we will confirm:
1. OS version of the phone that runs the Tether app.
2. MAC address of the WR845N (you can provide this via PM).