Promo without paid ads

If you launched a business and you were unable to do any paid adverts on google or social media, how would you get the word out?

I've got a referral program in place and post 1-2x per day on Twitter and Insta. (Feels like shouting into the void.)

I'm wondering if paid promo of big accounts might be the way to go.

What other ideas do you have for how to promote without using social media advertising?

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