How to validate?

I've read so much about coming up with ideas. And I have a couple. I want to validate them now. My question is, how do YOU go about validating your business idea? I know you can build a landing page, but how do you direct people to your site?? Are you paying for Sales Navigator? What's your go-to method?

I don't want to start building without being sure that it's a real problem, but I'm always so lost at this step. I feel like I could even try validating an EXISTING, SUCCESSFUL idea, and I would struggle. Hence this post.

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