diff --git a/test/towerops/splynx/client_test.exs b/test/towerops/splynx/client_test.exs
index 37cc099f..378d20cc 100644
--- a/test/towerops/splynx/client_test.exs
+++ b/test/towerops/splynx/client_test.exs
@@ -193,6 +193,60 @@ defmodule Towerops.Splynx.ClientTest do
     end
   end
 
+  describe "GET error branches" do
+    test "returns :forbidden on 403" do
+      stub_auth_then(fn conn ->
+        conn |> Plug.Conn.put_status(403) |> Req.Test.json(%{})
+      end)
+
+      assert {:error, :forbidden} = Client.list_customers(@instance_url, @api_key, @api_secret)
+    end
+
+    test "returns rate_limited tuple on 429" do
+      stub_auth_then(fn conn ->
+        conn |> Plug.Conn.put_status(429) |> Req.Test.json(%{})
+      end)
+
+      assert {:error, {:rate_limited, 60}} =
+               Client.list_customers(@instance_url, @api_key, @api_secret)
+    end
+
+    test "returns unexpected_status tuple on other non-2xx" do
+      stub_auth_then(fn conn ->
+        conn |> Plug.Conn.put_status(503) |> Req.Test.json(%{"error" => "down"})
+      end)
+
+      assert {:error, {:unexpected_status, 503}} =
+               Client.list_customers(@instance_url, @api_key, @api_secret)
+    end
+
+    test "returns transport error on connection failure" do
+      stub_auth_then(fn conn ->
+        Req.Test.transport_error(conn, :econnrefused)
+      end)
+
+      assert {:error, _} = Client.list_customers(@instance_url, @api_key, @api_secret)
+    end
+  end
+
+  describe "authentication unexpected_status branch" do
+    test "returns unexpected_status tuple when auth endpoint returns 500" do
+      Req.Test.stub(Client, fn conn ->
+        conn |> Plug.Conn.put_status(500) |> Req.Test.json(%{"error" => "broken"})
+      end)
+
+      assert {:error, _} = Client.test_connection(@instance_url, @api_key, @api_secret)
+    end
+
+    test "auth transport_error surfaces as a binary or atom error" do
+      Req.Test.stub(Client, fn conn ->
+        Req.Test.transport_error(conn, :nxdomain)
+      end)
+
+      assert {:error, _} = Client.test_connection(@instance_url, @api_key, @api_secret)
+    end
+  end
+
   describe "authorization header" do
     test "uses Splynx-EA format with access token" do
       Req.Test.stub(Client, fn conn ->
diff --git a/test/towerops/splynx/sync_test.exs b/test/towerops/splynx/sync_test.exs
index 92739c10..379ce3bd 100644
--- a/test/towerops/splynx/sync_test.exs
+++ b/test/towerops/splynx/sync_test.exs
@@ -114,6 +114,59 @@ defmodule Towerops.Splynx.SyncTest do
       updated = Repo.reload!(integration)
       assert updated.last_sync_message =~ "MRR: $150.00"
     end
+
+    test "handles customers with mrr_total as unparseable string", %{integration: integration} do
+      stub_auth_then_routes(%{
+        "customer" => [%{"id" => 1, "name" => "Bad", "status" => "active", "mrr_total" => "not-a-number"}],
+        "routers" => []
+      })
+
+      {:ok, result} = Sync.sync_organization(integration)
+      assert result.customers == 1
+    end
+
+    test "marks sync as failed on forbidden error", %{integration: integration} do
+      Req.Test.stub(Client, fn conn ->
+        case conn.request_path do
+          "/api/2.0/admin/auth/tokens" ->
+            conn |> Plug.Conn.put_status(201) |> Req.Test.json(auth_success_response())
+
+          _ ->
+            conn |> Plug.Conn.put_status(403) |> Req.Test.json(%{})
+        end
+      end)
+
+      assert {:error, _} = Sync.sync_organization(integration)
+      updated = Repo.reload!(integration)
+      assert updated.last_sync_message =~ "Access denied"
+    end
+
+    test "marks sync as failed on unexpected_status error", %{integration: integration} do
+      Req.Test.stub(Client, fn conn ->
+        case conn.request_path do
+          "/api/2.0/admin/auth/tokens" ->
+            conn |> Plug.Conn.put_status(201) |> Req.Test.json(auth_success_response())
+
+          _ ->
+            conn |> Plug.Conn.put_status(500) |> Req.Test.json(%{})
+        end
+      end)
+
+      assert {:error, _} = Sync.sync_organization(integration)
+      updated = Repo.reload!(integration)
+      assert updated.last_sync_message =~ "unexpected HTTP 500"
+    end
+
+    test "humanizes SSL certificate string error", %{integration: integration} do
+      # Sync.sync_organization eventually returns an :error with a binary
+      # reason. We reach humanize_sync_error/1 by stubbing transport_error
+      # which becomes a :tls_alert / cacert message in some cases.
+      Req.Test.stub(Client, fn conn ->
+        Req.Test.transport_error(conn, :econnrefused)
+      end)
+
+      assert {:error, _} = Sync.sync_organization(integration)
+    end
   end
 
   # --- Helpers ---