Set People Picker field in a SharePoint List Item using Microsoft Graph

When we want to use MS Graph to add an item into a SharePoint List that contains a People Picker, then here what needs to be done:

1. Retrieve the Site ID for the root site collection, using https://graph.microsoft.com/v1.0/sites/[CORP].sharepoint.com:/sites/MySiteCollection
2. Retrieve the Site ID for the target end website, using https://graph.microsoft.com/v1.0/sites/[CORP].sharepoint.com:/sites/MySiteCollection/MyParentSiteWeb/MyTargetWebsite/
3. Use the user’s email address to retrieve the SharePoint User ID of that person from the User Information List, using https://graph.microsoft.com/v1.0/sites/[ROOT_SITE_ID]/lists/User%20Information%20List/items?expand=fields&filter=fields/EMail%20eq%20'[ENCODED_EMAIL]'&top=1" – the email must be encoded to be passed in an URL
4. If the user doesn’t exist in this SharePoint yet, then you have to use the REST API call to https://[CORP].sharepoint.com/sites/MySiteCollection/MyParentSiteWeb/MyTargetWebsite/_api/web/ensureUser with the payload {"logonName":"user_email@corp.com"} – you should get the User ID this time
5. Then we need to get the List ID of where we want to add the item, using https://graph.microsoft.com/v1.0/sites/[TARGET_SIDE_ID]/lists/[LIST_NAME_ENCODED]
6. Finally, we can add the item using https://graph.microsoft.com/v1.0/sites/[TARGET_SIDE_ID]/lists/[TARGET_LIST_ID]/items with a specific value depending if it’s a multi-selection people picker field or not – let’s say the internal name for my field is “Requestor_x0020_Name”, then I have to append “LookupId” to this name:
   • for a single selection field, the payload contains:

     {"Requestor_x0020_NameLookupId": "[USER_ID_FOUND_WITH_GRAPH]"}

   • for a multi-selection field we have to pass the odata type, and put the User ID into an array, then the payload contains:

     {
     "Requestor_x0020_NamesLookupId@odata.type":"Collection(Edm.String)",
     "Requestor_x0020_NamesLookupId": [ "[USER_ID_FOUND_WITH_GRAPH]" ]
     }