Buying a cocktail for a lady seems like a magical ritual that should definitely help seduce a lady in a bar, or vice versa, some guys think that after buying a drink, a girl will look at you exclusively through the prism of "sugar daddy".
When heading to a bar, never fool yourself with should or shouldn't. If you have drawn up a scenario for yourself how your communication with a girl should go, then believe me, a maximum of 5% of what you thought of yourself will happen, and those very 5% will become your prepared phrases that you can say as uncertainly as possible.
Let's look at a few examples:
You saw a lady who inspired you to a feat and now you decide to approach. Suppose she already has a drink that she just had time to taste, you won't shout to the bartender to prepare another one for this beauty who is next to you. In this case, of course, there is no point in buying a cocktail.
If you struck up a conversation and you see that a lady is showing interest in you, and you liked her herself, why not ask her when she finishes her cocktail, "What is this delicious you drink? I also want to try" and order two of these cocktails at the bar.
It all depends on the situation in which you find yourself, take the most appropriate and hateful actions and use a tool such as a cocktail, but do not regard it as your ticket to a happy relationship.
If you don't like the lady, then there is no point in wasting your time. Get to know another person for whom you will enjoy doing something, including buying her favorite cocktails.
Also, do not be stingy, this is just a cocktail, treat them to a girl if she wants it, it will only add points to you.