What you are being prompted for is the WEP or WPA encryption key as set up in the router's wireless security settings. It isn't the same thing as the 'password' used to access the router's configuration pages if that's what you're trying to enter.
Surface Pro (2017) vs Surface Pro 4
20 groundbreaking 3D animation technologies coming to Siggraph 2017
iPad Pro 12.9 vs Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.