While making a new account in the app, enter a 10-digit phone number. If you don't have an Indian number (starting in +91) just use a fake 10-digit number.
3.
Create any 4-digit PIN code.
4.
When choosing facilities, pick any of the "Demo" facilities (e.g.: Demo Facility A, Demo Facility B etc.)
The Sandbox app
Sandbox app is only accessible to the Contributors team, and you have to be invited to see it on the Play Store. We deploy a new version of Sandbox to the Store every night, automatically.
Ask someone from the Contributors team to give your Play Store email address access to the app. Unless this happens, you will not be able to find the app on the Store.