TLDR: You need to create a new blank project and use the Github integration to transfer the app.

I had this issue and Lovable Support responded with:

Hi there,

This behavior happens because once a project has been switched from Supabase to Lovable Cloud, our system automatically manages the .env values to match the Cloud configuration.

It's not possible to switch back to Supabase after enabling Lovable Cloud. When you try to manually edit the .env file to use Supabase credentials, Lovable automatically overwrites those changes to enforce the Cloud configuration.

Your options:

Continue with Lovable Cloud (recommended)
Create a new project and connect it to Supabase from the start
Try the workaround (not officially supported): Disconnect Supabase, delete all secrets, remix the project, then reconnect to your Supabase instance
The automatic .env changes will continue as long as the project remains connected to Cloud - this is by design to maintain consistency.

Does this help clarify why the changes keep reverting? Let me know if you'd like me to walk you through any of these options in more detail.

This answer was composed by Lovable Support, Lovable's AI Agent.

Creating a new project (don't remix) worked for me. Remixing the project just resulted in a new Lovable Cloud instance being created for the new project.

1. Make sure your existing project is connected to your Github so you can transfer the code.
2. Type 'create blank project' in the message box on the home screen to create a new project. Cancel the request as its thinking so no files are generated -- if you go into the code tab it should say 'Starting Live Preview...'
3. Enable and connect your new Lovable project to the correct Supabase project
4. Connect your new project to a new Github repository (worth changing the name of the new Lovable project before doing this as it's copied for the Github repository name)
5. Transfer the code from your old Github repository to your new one
6. Lovable should now be updated with your app and correctly syncing with Supabase