Update Business form documentation (#784)

* add text area mention on datasource update

* Updates

* Update data-flow.mdx

* Update data-flow.mdx

---------

Co-authored-by: Mikhail Volkov <[email protected]>

docs/business-forms/data-flow.mdx

@@ -164,6 +164,64 @@ We simplified work with the payload creation. The Business Forms panel has a des
   src="/img/blog/2024-07-02-form-panel-4.0.0/update-payload.png"
 />
 
+### Use Text Area with multiple lines
+
+Text Area element allows you to create text with multiple lines:
+
+<Image
+  title="Text Area element with multiple lines."
+  src="/img/plugins/business-forms/text-area-multiline.png"
+/>
+
+After entering the data and submitting the form, you may see a data source error. The issue is caused by not properly processing and converting multiple lines in the payload.
+
+<Image
+  title="Data source update error with multiple lines."
+  src="/img/plugins/business-forms/datasource-error-update.png"
+/>
+
+To avoid this behavior, please add following steps in the Create Payload code editor:
+
+- Find element refer to the TextArea element.
+- Add replace logic to value `payload[element.id] = element.value.replaceAll("\n", "\\n");`
+
+#### Code example
+
+```js
+const payload = {};
+
+context.panel.elements.forEach((element) => {
+  if (!element.value) {
+    return;
+  }
+
+  /**
+   * Required logic to update the value
+   */
+  if (element.id === "description") {
+    payload[element.id] = element.value.replaceAll("\n", "\\n");
+    return;
+  }
+
+  payload[element.id] = element.value;
+});
+
+/**
+ * Check payload using developer tools
+ */
+console.log("update payload:", payload);
+
+/**
+ * Data Source payload
+ */
+return payload;
+```
+
+<Image
+  title="Create payload code editor with custom payload to update multiple lines."
+  src="/img/plugins/business-forms/datasource-create-payload-code-editor.png"
+/>
+
 ### REST API
 
 See the description for the Initial Request REST API. Both Initial and Update requests have the same parameters. Also similarly, you can use global and dashboard variables in the API server call along with header parameters.