How do you get 1:1 calls during validation stage?

by mzietek

I work on my 3rd startup, previous projects had poor product-market fit so I'm trying to do my best when validating.
I was doing Twitter DMs, LinkedIn + hunter.io and sending emails, Reddit DMs and even Polywork DMs. I managed to get +20 sign-ups for http://focusity.space/ and I had a lot DM conversations with target users.

I think that the most powerful way to understand customer needs is to get someone on 15 min call, but I find it super-hard to do it.
Most of people I talk to say that they don't have time and ask me to send questions on DMs but imo it's not the same. I also had a lot of no-show-offs so even when I managed to schedule a call, I still didn't get any feedback.

How do you contact people to have 1:1 calls? (channels)
What message do you send them?
How many 1:1 calls did you have before building MVP?