So I tried to reach out to more customers. I managed to help a few store owners to improve their websites. And I got more people using the app. But overall, I think that this image optimizer idea is not worth pursuing anymore.
Because there are too many competitors in this niche, and all of them are doing the same. Just a different design and pricing models, but overall it's the same app with the same functionality.
And it's not a recurring problem in most cases, people adding products, but not so often.
The first mover(app) took everything.
Besides that, there is a problem with Shopify payouts as a non-US resident. It is hard to get money(payouts). In Ukraine(where I live), for example, it's not possible to receive money via PayPal(it's a shame).
I contacted customer support, and they said that if I want to receive money(as a Shopify partner), I need to contact support and they will send it manually to my bank account. Funny right?