fix(OpenAI Node): Fix issue with expressions not working with chat complete (#5609)

packages/nodes-base/nodes/OpenAi/ChatDescription.ts

@@ -1,4 +1,5 @@
 import type { INodeExecutionData, INodeProperties } from 'n8n-workflow';
+import { chatBodyPresend } from './ChatFunctions';
 
 export const chatOperations: INodeProperties[] = [
 	{
@@ -114,7 +115,7 @@ const completeOperations: INodeProperties[] = [
 			send: {
 				type: 'body',
 				property: 'messages',
-				value: '={{ $parameter.prompt.messages }}',
+				preSend: [chatBodyPresend],
 			},
 		},
 	},

packages/nodes-base/nodes/OpenAi/ChatFunctions.ts

@@ -0,0 +1,14 @@
+import type { IDataObject, IExecuteSingleFunctions, IHttpRequestOptions } from 'n8n-workflow';
+
+export async function chatBodyPresend(
+	this: IExecuteSingleFunctions,
+	requestOptions: IHttpRequestOptions,
+): Promise<IHttpRequestOptions> {
+	const prompts = this.getNodeParameter('prompt', '{}') as IDataObject;
+
+	requestOptions.body = Object.assign({}, requestOptions.body, {
+		messages: prompts.messages,
+	});
+
+	return requestOptions;
+}