Regarding app release

I am new to okta. My app is released on play store. Some of the client want to distribute the app using okta. So I want to to release my app on OIN platform. Do I need to purchase OMM feature.

You do not need a license to submit an application to the OIN
The guide for this can be found at https://developer.okta.com/docs/guides/submit-app/openidconnect/overview/