Graph API Call Issues - POST Event - api

Question

I'm running into issues when trying to create an event in a specific user calendar.
This call works fine: POST https://graph.microsoft.com/v1.0/me/events
But when I change the API Call to include the other user details, it throws this error: "The specified object was not found in the store."
I have created an app on Azure and assigned all necessary permissions.
App Permissions
Error:
Can someone please assist if I'm missing something?

Answer 1

Please note when you use /me, it means you are calling the ms graph api with a delegate api permission which is authentiated by entering user name/password, you can only do operations on your own account with this kind of authentication. While you want to do operations for other users like /users/user_id/xxx, you required the application api permission. That's why api document showed api permission in Delegated and Application. One for personal and another for all users.
When we need to get access token contain application permission, we need to use client credential flow. This flow is used for daemon application since this kind of application doesn't have user interactive operation, so we can only use application permission for this kind of scenario. And as you can see it will offer "very big ability" to the application(allow application to create/change/delete items for any user in your tenant), so we need to use appliation permission with caution.
Come back to the case, you can follow this section to generate access token and call the api. You can also using graph SDK in your code to call that api.
using Azure.Identity;
using Microsoft.Graph;
public async Task<string> testAsync() {
var scopes = new[] { "https://graph.microsoft.com/.default" };
var tenantId = "tenant_name.onmicrosoft.com";
var clientId = "azure_ad_clientid";
var clientSecret = "client_secret";
var clientSecretCredential = new ClientSecretCredential(
tenantId, clientId, clientSecret);
var graphClient = new GraphServiceClient(clientSecretCredential, scopes);
var a = await graphClient.Users["user_id"].Request().GetAsync();
return a.DisplayName;
}