docker-compose exec snipe-it php artisan key:generate
Notes:
Add that APP_KEY to your docker env-file (we left a placeholder for it in your starting docker env file, above). Make sure to include the base64: prefix if it is given! If you're not using an env-file, you will need to pass the APP_KEY as an environment variable to your docker container.
Replace placeholder in APP_KEY=<<Fill in Later!>>
with the key you get, don't forget to bring the base64: prefix.
After you set the key here is you can run the app
# run the app on detach mode
docker-compose up -d
# see the logs
docker-compose logs -f snipe-it # snipe-it
For more information see this document.