Add Call external action

content/en/docs/refguide/modeling/application-logic/microflows-and-nanoflows/activities/integration-activities/call-external-action.md

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+---
+title: "Call external action"
+url: /refguide/call-external-action/
+tags: ["studio pro", "integration activity", "call external action"]
+weight: 5
+#If moving or renaming this doc file, implement a temporary redirect and let the respective team know they should update the URL in the product. See Mapping to Products for more details.
+---
+
+{{% alert color="warning" %}}
+This activity can only be used in **Microflows**.
+{{% /alert %}}
+
+## 1 Introduction
+
+The **Call external action** activity allows you to call an external action that is defined by an OData service that your app consumes. You can configure the values that are passed as parameters, and how the value that is returned by the external action should be handled.
+
+## 2 Properties
+
+An example of call external action properties is represented in the image below:
+
+[ image: TODO ]
+
+There are two sets of properties for this activity, those in the dialog box on the left, and those in the properties pane on the right.
+
+The call external action properties pane consists of the following sections:
+
+* [Action](#action)
+* [Common](#common)
+
+## 3 Action Section {#action}
+
+The **Action** section of the properties pane shows the action associated with this activity.
+
+You can open a dialog box to configure this action by clicking the ellipsis (**…**) next to the action.
+
+You can also open the dialog box by double-clicking the activity in the microflow or right-clicking the activity and selecting **Properties**.
+
+The properties dialog box consists of four tabs:
+
+* [General](#general)
+* [Public documentation](#public-documentation)
+
+## 4 General Tab {#general}
+
+### 4.1 Action
+
+On the top of the General tab you will find the **Action** property, which contains the selected external action that will be called. By clicking **Select...** a selector dialog will pop up, which allows you to select an action from any external service that you have consumed in your app.
+
+After selecting an action, Studio Pro will verify if the types that are used by the parameters and the resulting return value of the external action are available in your project. If a parameter or the return value has an enumeration type which is not yet consumed in your project, it will be created for you. If a parameter or the return value is an object or a list of an external entity type that is not yet part of your domain model, it will ask you to confirm consuming this external entity. When you confirm this by clicking **Ok**, the necessary external entities will be added to the domain model of the same module as the current microflow you are editing. If you hit **Cancel**, the action will not be selected. 
+
+### 4.2 Parameters
+
+In the table below the selected action, you will find the parameters that are defined by the external action, with its name, its type, and the provided argument.
+
+Selecting a row in the table and hitting **Edit parameter value**, or simply double-clicking it, will show you the [Edit External Action Parameter Mapping](#edit-parameter-mapping) dialog, where you can edit the argument that will be passed when calling the external action.
+
+For each parameter in the template, you can specify its value using a [microflow expression](/refguide/expressions/) resulting in a string value. This value will be inserted at the position of the parameter.
+
+## 5 Public Documentation Tab {#public-documentation}
+
+In the **Public documentation** tab, you can find a **Summary** and a **Description**. These fields contain documentation provided by the author of the service.
+
+## 6 Edit External Action Parameter Mapping Dialog {#edit-parameter-mapping}
+
+[ image: TODO ]
+
+The **Edit External Action Parameter Mapping** dialog allows you to set the value of an external action's parameter. You can either select a **Variable** from the dropdown field, or write a custom **Expression**. 
+
+Note that a parameter should always pass a value to the external action. When **Can be empty** is true, the selected variable or expression used may evaluate to `empty`. When it is false however, the microflow will throw an error when it attempts to pass a value that evaluates to `empty` to the external action.