Founders: How did you acquire your first 100 users?

I recently launched a product and would love to hear from founders who have already reached their first 100 paid users.

What strategies worked best for you?

Where did your first customers come from?

What were the biggest challenges in the early stages?

Was there a particular channel, decision, or turning point that helped your product start gaining real traction?

Would love to hear what worked, what did not, and what you would do differently if you were starting again.