.env.project identifier
The .env.project file uniquely identifies your project at sync.dotenv.org. You SHOULD commit this file to source control. It is safe to do so. Aside: DON'T commit your .env or .env.me to source control.
You can think of it like a unique git url at GitHub. It identifies your project so that your teammates pull the correct .env file from sync.dotenv.org.
Example
Here's an example of what the .env.project file looks like:
DOTENV_PROJECT=prj_ac17b953484388fcdc1b35bb01e7506fd1e739378d4c2b0ee6be968963564cb8The first thing you might notice is the formatting is the same as a .env file. This is intentional to allow for maximum future interoperability.
The DOTENV_PROJECT key is important. It is required. It is that value that identifies your project uniquely to the Dotenv syncing mechanisms.
Generating
You can generate a .env.project file at ui.dotenv.org or through the dotenv cli tool. The process is similar to creating and cloning your very first git repo on GitHub.