Ask HN: How to convince partner to sell

I've got some experience building building SaaS apps, and about 2 years ago was approached by a client with an idea for a new app.

He had the industry knowledge for the app, and I had the technical knowledge to build it. We spent about 6 months building the project (including hiring another developer), with each of us putting in equal amounts of money. In terms of time, I definitely spent more time in building the product, with the expectation that he would do more of the marketing when the time came.

The product itself has done OK with almost no marketing, but we both see more potential in it. Unfortunately, we've let it stagnate over the past year or so for a few reasons

I feel like I would put much more time and energy into the product if it was my own, but unfortunately my partner does not want to sell his share. Although there is no animosity, we don't work that well together.

Any ideas on how I can convince him to sell his share?