You can also try logging in through the extender’s web interface with a browser, that sometimes works better than just relying on the app. If it still doesn’t work, a reset might help. Even though the Tether app uses the cloud and doesn’t require you to be on the same Wi-Fi, for the web interface you’ll need to connect directly to the extender’s network

Hello @AnnoyedofLaxey , 

Welcome to our community.

 

If you cannot log in to the management page of the RE315 via Web and Tether App, please try the suggestions of Vendex.

 

If your devices are having trouble connecting up to the extender's Wi-Fi, the following steps can be useful:
    1. Ensure the device can connect to the router's Wi-Fi without issue. 
    2. Ensure the wireless password is correct. 
    3. Reboot the device and the extender. 
    4. Forget the extender's Wi-Fi on the device and try reconnecting to it. 
Note: If the range extender's Wi-Fi password is super long with numbers and letters or the extender, and it cannot be connected using the router's wireless password, please hard reset the extender and reconfigure it via the Tether app:How to configure Range Extender via Tether APP.