Microsoft Graph API - /drive/root/children always empty, even though I have files in my onedrive - rest

Question

I'm trying to use the Microsoft Graph API to List Children by Getting access without a user
I have built my URL as you would expect:
https://graph.microsoft.com/v1.0/edffcd1c-e5b2-42f2-b554-XXXXXXXXX/drive/root/children
Where edffcd1c-e5b2-42f2-b554-XXXXXXXXX is the user ID of whom I'm trying to list the files.
Yet when I call this I get an empty result every time:
{
"#odata.context": "https://graph.microsoft.com/v1.0/$metadata#drive/root/children",
"value": []
}
Why is that?
UPDATE: It seems that this API is only returning files from the Sharepoint account... not the OneDrive account. I already have access to the Sharepoint files from the Sharepoint API's themselves. Is there a way to get OneDrive files from the Microsoft Graph API?
This URL https://dev.onedrive.com/README.htm seems to state that we should be able to do this.

Answer 1

Is there a way to get OneDrive files from the Microsoft Graph API?
Yes, there is: you must use the scope Files.Read.All or Files.ReadWrite.All
then, your requests to /drive/root/children will no longer return an empty array.

Answer 2

I just had a typo in the User:
https://graph.microsoft.com/v1.0/edffcd1c-e5b2-42f2-b554-XXXXXXXXX/drive/root/children
was supposed to be
https://graph.microsoft.com/v1.0/users('edffcd1c-e5b2-42f2-b554-XXXXXXXXX')/drive/root/children

Answer 3

You can also use this endpoint
https://graph.microsoft.com/v1.0/me/drive/root/children
and pass authorization header Bearer Token

Answer 4

There are two things:
1) First check if the user has given the permission for
Files.Read.All or Files.ReadWrite.All
2) The following endpoint didn't work for business account
/drive/root/children
I changed it to
/drives/{drive_id}/root/children
and it worked fine. Please check.