Cant sell items Please Help

Okey so i started to play lol few days ago and when i enter the shop and buy an item i cant sell it the sell button is grey i can undo a newly bought item but no sell this is very annoying in late game when i have bad items and cant get rid of them does anyone have a solution to this problem please help

i have been able to sell once but now i cant

and befor you ask me if i pressed the item befor trying to sell it or if im in fountain yes i know how to sell an item but the sell button is grey cant click it

I have searched for a solution but i cant find it and no its my resolution i can see the sell button