There seemed to be rapid growth and interest. Getting any revenue is hard - growing from 700/month to 7000/month can be mostly momentum. Just sitting on it would make more.
Maybe there is more to the story but if not, please hold out with your next project. You'll get low ballers.
I had someone offer me 30k for an app I spent a month building. I would have taken it but he wanted to do a payment plan and I said no way. The project has since grown without much help from me to ~2.5k/month and will likely continue for years. It already made more than the offer.
The ability to sell it is still there at any time and for more money just from the momentum of growth. Once you sell, though, you stop collecting revenue and having the potential of growing it even bigger.
If someone wants it at first, it's likely worth more than they're offering. They know it and you should, too.