You may just want to question your general approach of doing things. If you're going up to as many girls as possible trying to get their phone numbers it's unlikely that you'll get into a long interaction, simply due to the fact that you're deliberately going up with the need to make something happen.

It's a bit hard to explain, but there's a million variables when you're interacting with people other than just the content of 'what you say'. Body language, the context of when you go up, your vibe, general random shit you can't know. This is why you hear contradicting information about the content of what works. Some guy might do awesome being high energy jumping around the place, some people might be super articulate. Personally my game is very chill and non committal. Different things work for different people and that's something you figure out through trying different shit until you relax into your own natural way of behaving.

A big issue with PUA people and the whole 'I don't know what to say' thing, is that they set the bar way too high, both in what they feel they should say and in the reactions they think they should be getting. There's this preconception that if you flip all the right switches by being super cool and interesting you'll get super positive feed back and everything will move forward super quick, like if you did everything by the PUA book she'd just drop trou and fuck you right there. At first guys go in, don't get a quick positive reaction so they bail early. Then after a while they go in, get an okay reaction, try to move shit along to quick and either bail too early or freak people out.

This mentality can manifest itself in subtle ways, like you give off this odd sense of thirsty urgency that people can sense and it makes them feel uncomfortable talking to you. If you've ever been out in a club with a group of girls and seen guys hitting on them you'll know what I mean, and what a relief it is when people just act normal.

The reality is, long interactions are what you want to be getting. They have peaks and troughs. You won't always be interesting, she won't necessarily be super interested the whole time. That's alright. Practise staying in conversations for longer without feeling the need for something to happen. Practise lowering the bar for what you feel you need to say. Hit up groups multiple times. Above all, take your time and chill.