Vinegar and battered chicken? I made a recipe for crispy shallow-fried battered chicken. The recipe called for a little vinegar to be added to the chicken after drying and seasoning. This dish did not work, the batter (just flour and water) slipped off the chicken in the oil because the meat was too wet. What is the reason for the vinegar here? Is there a trick to this or do I just have a bad recipe?
Adding vinegar 'to the chicken' might give it a slight tanginess, but its certainly going to cause issues with the  batter adhesion.  Sounds like a bad recipe (especially if your batter was just flour and water too!).

Every time I've seen vinegar in batter dipped chicken, its because there's also baking soda and it helps produce a lighter, airier batter.  And you put it in the batter, not on the chicken.