Hey, happiness evolutions are currently bugged if you either denied the evolution at max happiness once or got it to max happiness during the wrong day time for example. To fix the issue for your Golbat you simply need to faint your Golbat in a wild battle and heal it in a pokecenter. Then get it to max happiness again (via wild battles for example). Happiness evolutions usually dont require a level-up, they only need to reach max happiness to evolve.
If you should still struggle to get to evolve you could try to use a mysterious candy which evolves a pokemon even if its at level 100 as long as you meet the requirements needed for the evolution. You can purchase mysterious candies in all four department stores (Celadon, Goldenrod, Lilycove, Veilstone) for 5k pokedollars, for 2 PvE coins at PvE Coin Masters or for 1 PvP coin at PvP Coin Masters.