Why does the connection not work?

When I enter the WLAN password on the TV at TIMvision so that I have access to youtube, Netflix etc. It always says: Connection with (name of WLAN) not possible. Cables are all where they belong and I entered the password correctly.
Can someone help?

Lg

Router configuration (e.g. MAC filtering, only known devices, …)
Read the operating instructions for the television (as no model was named here)