prevent user from creating multiple accounts

i’m developing an android app using unity that requires and account to use it.
the problem is that i need to prevent users from creating multiple accounts and i didn’t find a solution for that. i tried DeviceUniqueIdentifier but it generates a new id if the user uninstall the app and reinstalled again.

How are you creating the account? I just save emails as usernames and require those to be unique on my backend. Currently I’m using MongoDB with expressJS/NodeJS on the backend and when creating a new user account I just query the DB to ensure the email address is unique. I don’t use unique device identifiers because the device could be sold to another person in the future or another person could want to use it, also the person who creates the account will likely upgrade the device in the future and the unique device ID will then be different. But if you want you can use SystemInfo.deviceUniqueIdentifier which apparently guarantees to return a unique device id string.