Transfer app 🛒

Hi Gliders,
I built an app, completed the pro version for it. Now I want to transfer it somehow to another account and have him pay for it.
What can be done in such a situation?

Another question, I have videos from YouTube links in the app. A customer told me that after 30 seconds the phone turned off and the video stopped.

Is there a way to fix this (regardless of phone settings)

Thanks for the helpers

Regarding the video, is the user on iOS?