I'm not alone, I put together a small team of experienced developers.
As for motivation, in the first few days we gave out 20 promo codes, there were winners, they got the winnings but they didn't write reviews....
Maybe it's time to think about the fact that before receiving the prizes, users have to write a short review about the user experience and then have the option to withdraw the prizes, but not before. That way, the benefit would go both ways and potential users would be able to know the qualities of the service before they even use it. It shouldn't be that way, as users, as a thank you for those promo codes you've shared, should write the reviews. But we already know what people are like, unfortunately...
that would be great.

but none of them, before taking the promo code, did not make a promise to write a review, respectively, and did not break the promise.
Now we are doing some work, after which we will hold new promotions, promo code in exchange for a review.