If a girl isn't responding quickly, or even not at all, you need to change your texts.
Also don't forget to mix up the amount of time it takes for you to text back. Don't always wait for a while. Sometimes you gotta fire back right away & get into that rapid fire reply mode.
But if a girl isn't responding, then she's most likely bored. Or just not interested.
Make your texts fun. Be different from everyone else texting her.
And if she still isn't replying.... Then let it go & text the next girl.