Microsoft Graph SharePoint access items (read/write) - microsoft-graph-api

Question

I am attempting to create a new list item in SharePoint Online using the [beta] Microsoft Graph endpoint. The goal is to call Microsoft Graph from an Outlook Add-in but the problem persists on Postman.
When I call the endpoint as per the documentation I get the following error message:
{
"error": {
"code": "unauthenticated",
"message": "The caller is not authenticated.",
"innerError": {
"request-id": "bb094f39-71c9-4c7d-9d9b-913cc9622baf",
"date": "2017-08-08T11:32:02"
}
}
}
I'm using ADAL JS to fetch the authentication token and I initialized my AuthenticationContext with my tenantID. My app has the following permissions: offline_access, Sites.Read.All, Sites.ReadWrite.All, User.Read
2nd Edit - more details on readItem
I use the https://graph.microsoft.com/beta/sites/{site-id}/lists/{list-id}/items endpoint with the {site-id} of my desired site from /sites and the {list-id} of the list from /sites/{site-id}/lists but this is the empty response I get:
{
"#odata.context": "https://graph.microsoft.com/...",
"value": []
}
If I try to to add /{item-id} to my original call to access specific item I receive this response:
{
"error": {
"code": "itemNotFound",
"message": "The specified list was not found",
"innerError": {
"request-id": "6e7ccae3-3aee-4dbb-ae3e-de61250478e0",
"date": "2017-08-09T13:13:33"
}
}
}
Which doesn't make sense because I can retrieve valid information about the list if i make the call without /items/..
Any and all input appreciated :) I'll gladly provide more code, this is all I deemed relevant and didn't want to overcrowd the post.

Answer 1

might be that you actually don't have an item with that id, since https://graph.microsoft.com/beta/sites/{site-id}/lists/{list-id}/items/1 works for me.
test the id's you really have by just https://graph.microsoft.com/beta/sites/{site-id}/lists/{list-id}/items and each item returns it's id.