dataverse_lookup_bind.cs

using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;

public class DataverseLookupBindExample
{
    public static async Task Main()
    {
        var environmentUrl = "https://yourorg.crm.dynamics.com";
        var accessToken = "YOUR_ACCESS_TOKEN";
        var contactId = "CONTACT_GUID";
        var accountId = "ACCOUNT_GUID";

        using var client = new HttpClient();
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        client.DefaultRequestHeaders.Add("OData-Version", "4.0");
        client.DefaultRequestHeaders.Add("OData-MaxVersion", "4.0");

        var payload = $$"""
        {
          "parentcustomerid_account@odata.bind": "/accounts({{accountId}})"
        }
        """;

        using var content = new StringContent(payload, Encoding.UTF8, "application/json");
        var response = await client.PatchAsync(environmentUrl + $"/api/data/v9.2/contacts({contactId})", content);
        response.EnsureSuccessStatusCode();

        Console.WriteLine($"Linked contact {contactId} to account {accountId}");
    }
}