Different behavior between graph explorer and calling the API directly

I authenticate with ADAL and get a token. Then I create a header like this:

headers = {
'User-Agent' : 'SharepointBridge/1.0',
'Authorization' : 'Bearer %s' % (tk),
'Accept' : 'application/json',
'Content-Type' : 'application/json'
}

Where tk contains my token.

My request to Graph is done like that:

r = requests.get('https://graph.microsoft.com/beta/sites/XXXXXXX.sharepoint.com,XXXXXX,XXXXXXX/lists/{list_id}/items',  headers = headers)

I can query anything below "items". But /items returns:

{
"@odata.context": "https://graph.microsoft.com/beta/$metadata#sites('XXXXXXXsharepoint.com%2CXXXXXX%2CXXXXXX')/lists('{list_id}')/items",
"value": []
}

If I do the exact same query in Graph Explorer, I get my list with all the information, not an empty value.