What actually kept users around after your launch day spike?

Launch day is exciting, but traffic can fade fast. For those of you who’ve launched, what did you do in the first 15-30 days that made the biggest difference to retention and expansion of user base?

I’m especially curious whether things like free credits or referral rewards moved the needle for you, or whether community and onboarding mattered more. I'm thinking of going down the free credits route but would love some inputs.

Would love to hear what worked and what didn't.