Explanation
Initialization
Whenever a configuration's backend changes, you must run terraform init again to validate and configure the
backend before you can perform any plans, applies, or state operations.
When changing backends, Terraform will give you the option to migrate your state to the new backend. This
lets you adopt backends without losing any existing state.
To be extra careful, we always recommend manually backing up your state as well. You can do this by simply
copying your terraform.tfstate file to another location. The initialization process should create a backup as
well, but it never hurts to be safe!
https://www.terraform.io/language/settings/backends/configuration