@Redgie Hello,
May I know how about the Led status on range extender after installation when it says No host Network, what is the model of your Router, thank you.
1. Here is a guide to troubleshoot RE installation step by step, kindly give it a try and let us know if it works for you,
Has connected to TP-Link extender but no internet, what can I do?
https://community.tp-link.com/en/home/forum/topic/198516
2. For Dual Band Range Extender, if the App or Web says "No Host Connection", it's probably because the router's 5G is using the DFS channel, it is recommended to disable Band Steering on the router as the guide below and, change 5G channel to Band 1(36, 40, 44, 48)
https://www.tp-link.com/en/support/faq/3143/