I have a Canvas app which I shared with another user (let's call him User1). I have set User1 as Co-Owner. While User1 can access and use the app, he can't share it. When User1 tries to Share the App by selecting the user and clicking Share in the "Share {App Name}" page, he gets this

When User1 navigates to make.powerapps.com, he sees the app but there is an error message

Some info:
- App type: Canvas
- Data Source: SharePoint
- In a solution?: Yes
- Uses environment variables: Yes
- Uses Power Automate flows: Yes
- Unmanaged Solution: Yes
What are the things I should check? How do I resolve this? Thanks.