A reason for this is that you may have an existing service account, in order to delete this project you need to delete first by going to Service Accounts.
You may delete the service account by following the instructions below:
- Go to Studio
- Select Service Accounts under API Integrations in the menu on the left.
- Select the existing account and at the rightmost part of the screen, you may press the "X" button to remove the account.
- A pop-up reminder screen should appear and you may select "Remove"
That's it! You should be able to remove/delete your selected project in your organization.