3 Steps to troubleshoot pairing issue:
1. Make sure the selected WiFi network is 2.4G private WiFi network, and is not a public WiFi network requiring credential login on a web portal like the ones at airport.
2. Verify the entered WiFi password is right.
3. Move your Sense-U device close to your WiFi router and make sure you are able to connect to internet.
* If still no luck, refer to the latest User Manual here: Sense-U App->Setup->Help->User Manual.