Error while working with UV co-ordinates

Hello, I have been trying to work out with materials in Unreal Engine and have come across a problem. The course is done by Sjoerd de Jong. He is so adept at teaching the internal working of the materials. However, the material is showing an error. Can anyone please help me on what I am doing wrong and why is it saying so? Thank you.

https://scontent-bom1-2.xx.fbcdn.net/v/t1.0-0/p180x540/92948458_3363061070390787_3087202168579555328_o.jpg?_nc_cat=107