Hi my chansey has max happiness of 255 and I tried Luling it up in daytime but till it is not evolving what us the reason

What should I do now it 98lv now 

 

Hey, it will only try to evolve upon reaching the max amount of happiness. So you would need to faint it in a wild battle to lose some happiness first and then get it to the max happiness again. Happiness evolutions dont need a level-up for the evolution, its only about reaching the max happiness.