diff --git a/.github/workflows/auto-pr.yml b/.github/workflows/auto-pr.yml
index 78a21f5..43512b3 100644
--- a/.github/workflows/auto-pr.yml
+++ b/.github/workflows/auto-pr.yml
@@ -7,7 +7,7 @@ on:
       - master
 
 permissions:
-  contents: write
+  contents: read
   pull-requests: write
 
 jobs:
@@ -18,21 +18,14 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
 
       - name: Create Pull Request
-        id: cpr
-        uses: peter-evans/create-pull-request@v7
+        uses: repo-sync/pull-request@v2
         with:
-          token: ${{ secrets.GITHUB_TOKEN }}
-          commit-message: "Auto-created PR from ${{ github.ref_name }}"
-          title: "${{ github.ref_name }}"
-          body: |
-            This PR was automatically created from branch `${{ github.ref_name }}`.
-          branch: ${{ github.ref_name }}
-          base: main
-          assignees: ${{ github.actor }}
-          draft: false
-          delete-branch: false
+          source_branch: ${{ github.ref_name }}
+          destination_branch: main
+          pr_title: ${{ github.ref_name }}
+          pr_body: "This PR was automatically created from branch `${{ github.ref_name }}`."
+          pr_assignee: ${{ github.actor }}
+          github_token: ${{ secrets.GITHUB_TOKEN }}
 
diff --git a/lib/then.ex b/lib/then.ex
index 732b2cf..1327740 100644
--- a/lib/then.ex
+++ b/lib/then.ex
@@ -89,10 +89,11 @@ defmodule Then do
       Module.delete_attribute(env.module, :then)
       arity = length(args)
 
-      existing_functions = Module.get_attribute(env.module, :functions_with_then) || []
-      function_key = {function_name, arity}
+      validated_callback = validate_callback_format(then_callback, env)
 
-      if Enum.any?(existing_functions, fn {name, ar, _callback} -> {name, ar} == function_key end) do
+      existing_functions = Module.get_attribute(env.module, :functions_with_then, [])
+
+      if function_already_has_then?(existing_functions, function_name, arity) do
         raise CompileError,
           file: env.file,
           line: env.line,
@@ -100,7 +101,7 @@ defmodule Then do
                       "Only one @then per function is allowed."
       end
 
-      Module.put_attribute(env.module, :functions_with_then, {function_name, arity, then_callback})
+      Module.put_attribute(env.module, :functions_with_then, {function_name, arity, validated_callback})
     end
   end
 
@@ -108,27 +109,63 @@ defmodule Then do
     :ok
   end
 
-  defmacro __before_compile__(env) do
-    functions_with_then = Module.get_attribute(env.module, :functions_with_then) || []
+  defp function_already_has_then?(existing_functions, function_name, arity) do
+    Enum.any?(existing_functions, fn {name, ar, _callback} ->
+      {name, ar} == {function_name, arity}
+    end)
+  end
 
-    wrapped_functions =
-      functions_with_then
-      |> Enum.map(fn {function_name, arity, callback_name} ->
-        args = Macro.generate_arguments(arity, __MODULE__)
+  defp validate_callback_format(callback, env) do
+    case callback do
+      atom when is_atom(atom) ->
+        {:local, atom}
 
-        quote do
-          defoverridable [{unquote(function_name), unquote(arity)}]
+      {module, function} when is_atom(module) and is_atom(function) ->
+        {:external, module, function}
 
-          def unquote(function_name)(unquote_splicing(args)) do
-            result = super(unquote_splicing(args))
-            unquote(callback_name)(result)
-            result
-          end
-        end
-      end)
+      _ ->
+        raise CompileError,
+          file: env.file,
+          line: env.line,
+          description: "Invalid @then format. Expected :function_name or {Module, :function_name}, got: #{inspect(callback)}"
+    end
+  end
+
+  defmacro __before_compile__(env) do
+    wrapped_functions =
+      env.module
+      |> Module.get_attribute(:functions_with_then, [])
+      |> Enum.map(&generate_wrapped_function/1)
 
     quote do
       unquote_splicing(wrapped_functions)
     end
   end
+
+  defp generate_wrapped_function({function_name, arity, callback_spec}) do
+    args = Macro.generate_arguments(arity, __MODULE__)
+    callback_call = generate_callback_call(callback_spec)
+
+    quote do
+      defoverridable [{unquote(function_name), unquote(arity)}]
+
+      def unquote(function_name)(unquote_splicing(args)) do
+        result = super(unquote_splicing(args))
+        unquote(callback_call)
+        result
+      end
+    end
+  end
+
+  defp generate_callback_call({:local, function_name}) do
+    quote do
+      unquote(function_name)(result)
+    end
+  end
+
+  defp generate_callback_call({:external, module, function_name}) do
+    quote do
+      unquote(module).unquote(function_name)(result)
+    end
+  end
 end