Nice one. Good to learn about polar.sh as a MoR alternative to Paddle.

I would prefer if it had a more leightweight htmx approach, but I guess it would be useful to some people.

Totally valid. The Go backend is just a REST API with no Next.js coupling. You could swap the frontend for Go templates + htmx without changing the backend at all. And yeah, Polar.sh has been great. Merchant of Record means I don't think about tax compliance.