diff --git a/ex/lib/logflare_ex.ex b/ex/lib/logflare_ex.ex
index d5b4669..31f1152 100644
--- a/ex/lib/logflare_ex.ex
+++ b/ex/lib/logflare_ex.ex
@@ -60,7 +60,22 @@ defmodule LogflareEx do
   def send_events(%Client{source_token: nil, source_name: nil}, _batch), do: {:error, :no_source}
 
   def send_events(client, [%{} | _] = batch) do
-    body = Bertex.encode(%{"batch" => batch, "source" => client.source_token})
+    on_prepare_payload = Map.get(client, :on_prepare_payload)
+
+    prepared_batch =
+      if on_prepare_payload do
+        Enum.map(batch, fn event ->
+          case on_prepare_payload do
+            {m, f, 1} -> apply(m, f, [event])
+            cb when is_function(cb) -> cb.(event)
+            _ -> event
+          end
+        end)
+      else
+        batch
+      end
+
+    body = Bertex.encode(%{"batch" => prepared_batch, "source" => client.source_token})
 
     case Tesla.post(client.tesla_client, "/api/logs", body) do
       {:ok, %Tesla.Env{status: status, body: body}} when status < 300 ->
diff --git a/ex/lib/logflare_ex/client.ex b/ex/lib/logflare_ex/client.ex
index 6ac3381..390e951 100644
--- a/ex/lib/logflare_ex/client.ex
+++ b/ex/lib/logflare_ex/client.ex
@@ -41,6 +41,7 @@ defmodule LogflareEx.Client do
   - `:source_token`: Source UUID. Mutually exclusive with `:source_name`
   - `:source_name`: Source name. Mutually exclusive with `:source_token`
   - `:on_error`: mfa callback for handling API errors. Must be 1 arity.
+  - `:on_prepare_payload`: mfa callback or anonymous function for preparing the final payload before sending to API. Must be 1 arity.
   - `:auto_flush`: Used for batching. Enables automatic flushing. If disabled, `LogflareEx.flush/1` must be called.
   - `:flush_interval`: Used for batching. Flushes cached events at the provided interval.
   - `:batch_size`: Used for batching. It is the maximum number of events send per API request.
@@ -61,6 +62,7 @@ defmodule LogflareEx.Client do
     field(:source_token, String.t())
     field(:source_name, String.t())
     field(:on_error, list() | mfa(), default: nil)
+    field(:on_prepare_payload, list() | mfa(), default: nil)
     # batching
     field(:auto_flush, :boolean, default: true)
     field(:flush_interval, non_neg_integer(), default: @default_flush_interval)
@@ -79,6 +81,7 @@ defmodule LogflareEx.Client do
         source_name: get_config_value(:source_name),
         tesla_client: nil,
         on_error: get_config_value(:on_error),
+        on_prepare_payload: get_config_value(:on_prepare_payload),
         flush_interval: get_config_value(:flush_interval) || @default_flush_interval,
         batch_size: get_config_value(:batch_size) || @default_batch_size
       })
diff --git a/ex/lib/logflare_ex/telemetry_reporter.ex b/ex/lib/logflare_ex/telemetry_reporter.ex
index f34ddbc..76c57d2 100644
--- a/ex/lib/logflare_ex/telemetry_reporter.ex
+++ b/ex/lib/logflare_ex/telemetry_reporter.ex
@@ -60,14 +60,16 @@ defmodule LogflareEx.TelemetryReporter do
   def handle_attach(event, measurements, metadata, config) when is_list(config) do
     # merge configuration
     config_file_opts = (Application.get_env(:logflare_ex, __MODULE__) || []) |> Map.new()
-    opts = Enum.into(config, config_file_opts)
+
+    opts =
+      Enum.into(config, config_file_opts)
 
     payload = %{metadata: metadata, measurements: measurements}
     to_include = Map.get(opts, :include, [])
 
     filtered_payload =
       for path <- to_include,
-          String.starts_with?(path, "measurements.") or String.starts_with?(path, "metadata."),
+          String.starts_with?(path, "measurements") or String.starts_with?(path, "metadata"),
           reduce: %{} do
         acc -> put_path(acc, path, get_path(payload, path))
       end
diff --git a/ex/test/logflare_ex_test.exs b/ex/test/logflare_ex_test.exs
index 3578034..a713cc1 100644
--- a/ex/test/logflare_ex_test.exs
+++ b/ex/test/logflare_ex_test.exs
@@ -85,6 +85,38 @@ defmodule LogflareExTest do
     end
   end
 
+  describe "on_prepare_payload" do
+    test "triggered before payload is sent" do
+      pid = self()
+
+      Tesla
+      |> expect(:post, 3, fn _client, _path, body ->
+        %{"batch" => [event]} = Bertex.decode(body)
+        send(pid, {event.ref, event})
+        {:ok, %Tesla.Env{status: 500, body: "some server error"}}
+      end)
+
+      LogflareEx.TestUtils
+      |> expect(:stub_function, 2, fn data ->
+        %{different: "value", ref: data.ref}
+      end)
+
+      for cb <- [
+            {LogflareEx.TestUtils, :stub_function, 1},
+            &LogflareEx.TestUtils.stub_function/1,
+            fn data -> %{different: "value", ref: data.ref} end
+          ] do
+        client = LogflareEx.client(api_key: "123", source_token: "123", on_prepare_payload: cb)
+        ref = make_ref()
+
+        assert {:error, %Tesla.Env{}} =
+                 LogflareEx.send_events(client, [%{some: "event", ref: ref}])
+
+        assert_receive {^ref, %{different: "value", ref: _}}
+      end
+    end
+  end
+
   describe "batching" do
     setup do
       pid = start_supervised!(BatcherSup)
diff --git a/ex/test/telemetry_reporter_test.exs b/ex/test/telemetry_reporter_test.exs
index 9788498..ab379cf 100644
--- a/ex/test/telemetry_reporter_test.exs
+++ b/ex/test/telemetry_reporter_test.exs
@@ -119,6 +119,42 @@ defmodule LogflareEx.TelemetryReporterTest do
       assert event[:measurements][:latency] == [123, 223]
       refute event[:measurements][:other]
     end
+
+    test "handle_attach/4 with :on_prepare_payload with anonymous function" do
+      pid = self()
+      ref = make_ref()
+
+      Tesla
+      |> expect(:post, fn _client, _path, body ->
+        decoded = Bertex.decode(body)
+        send(pid, {ref, decoded})
+        {:ok, %Tesla.Env{status: 201, body: Jason.encode!(%{"message" => "server msg"})}}
+      end)
+
+      :telemetry.attach("my-id", [:some, :event], &TelemetryReporter.handle_attach/4,
+        auto_flush: true,
+        flush_interval: 50,
+        include: ["measurements"],
+        on_prepare_payload: fn payload ->
+          payload
+          |> Map.put(:message, "hello!")
+          |> Map.put(:test, payload.measurements.other)
+        end
+      )
+
+      :telemetry.execute([:some, :event], %{latency: [123, 223], other: "value"}, %{
+        some: "metadata",
+        to_exclude: "this field"
+      })
+
+      Process.sleep(300)
+
+      assert_received {^ref, %{"batch" => [event]}}
+      # other fields will be included
+      assert event[:message] == "hello!"
+      assert event[:test] == "value"
+      assert event[:measurements][:latency] == [123, 223]
+    end
   end
 
   # reporter