diff --git a/README.md b/README.md
index dee8100..fcaabe2 100644
--- a/README.md
+++ b/README.md
@@ -68,6 +68,20 @@ await client.Tests.UpdateAsync(test.SessionId!, new TestUpdate
 });
 ```
 
+### Recording an external result
+
+`POST /v1/tests` needs the `BrowserId` of the browser/device the test ran on:
+
+```csharp
+var browsers = await client.Browsers.ListAsync();
+await client.Tests.CreateAsync(new ManualTestCreate
+{
+    Name = "external result",
+    TestEnvironmentId = browsers[0].BrowserId,
+    Success = true,
+});
+```
+
 ## Pagination
 
 List endpoints return a `TestingBotPage<T>` (the items plus `meta`), or you can stream every item
diff --git a/src/TestingBot.Api/Clients/Requests.cs b/src/TestingBot.Api/Clients/Requests.cs
index 682a1f5..94ba26d 100644
--- a/src/TestingBot.Api/Clients/Requests.cs
+++ b/src/TestingBot.Api/Clients/Requests.cs
@@ -33,6 +33,12 @@ public sealed record ManualTestCreate
     /// <summary>The test name (required).</summary>
     public required string Name { get; init; }
 
+    /// <summary>
+    /// The <c>browser_id</c> of the browser/device the test ran on (from <c>client.Browsers</c>).
+    /// The API rejects the request without it ("test[test_environment_id] is missing").
+    /// </summary>
+    public int? TestEnvironmentId { get; init; }
+
     /// <summary>Whether the test passed.</summary>
     public bool? Success { get; init; }
 
diff --git a/src/TestingBot.Api/Clients/TestsClient.Writes.cs b/src/TestingBot.Api/Clients/TestsClient.Writes.cs
index 611f825..91bd3b8 100644
--- a/src/TestingBot.Api/Clients/TestsClient.Writes.cs
+++ b/src/TestingBot.Api/Clients/TestsClient.Writes.cs
@@ -71,6 +71,7 @@ public Task<bool> CreateAsync(ManualTestCreate test, CancellationToken cancellat
         ArgumentNullException.ThrowIfNull(test);
         var form = new FormContentBuilder()
             .Add("test", "name", test.Name)
+            .Add("test", "test_environment_id", test.TestEnvironmentId)
             .Add("test", "success", test.Success)
             .Add("test", "status_message", test.StatusMessage)
             .Add("test", "extra", test.Extra)
diff --git a/tests/TestingBot.Api.Tests/Clients/WriteClientsTests.cs b/tests/TestingBot.Api.Tests/Clients/WriteClientsTests.cs
index d33e58a..2110601 100644
--- a/tests/TestingBot.Api.Tests/Clients/WriteClientsTests.cs
+++ b/tests/TestingBot.Api.Tests/Clients/WriteClientsTests.cs
@@ -31,6 +31,27 @@ public async Task Tests_Update_sends_rails_form_and_success_as_one()
         mock.VerifyNoOutstandingExpectation();
     }
 
+    [Fact]
+    public async Task Tests_Create_sends_test_environment_id()
+    {
+        var (connection, mock) = TestConnectionFactory.Create();
+        mock.Expect(HttpMethod.Post, BaseUrl + "tests")
+            .WithFormData("test[name]", "external result")
+            .WithFormData("test[test_environment_id]", "32166")
+            .WithFormData("test[success]", "1")
+            .Respond("application/json", "{\"success\":true}");
+
+        var ok = await new TestsClient(connection).CreateAsync(new ManualTestCreate
+        {
+            Name = "external result",
+            TestEnvironmentId = 32166,
+            Success = true,
+        });
+
+        ok.Should().BeTrue();
+        mock.VerifyNoOutstandingExpectation();
+    }
+
     [Fact]
     public async Task Tests_Stop_and_Delete()
     {