DialogflowをAPIで操作しようとするとPERMISSION

前提・実現したいこと

Node.jsで実装しているプログラムからAPIでDialogflowを呼び出そうとしております。
プログラムを実行すると、PERMISSION_DENIEDエラーが表示されます。

発生している問題・エラーメッセージ

Sending Query: Hello
Error: 7 PERMISSION_DENIED: IAM permission 'dialogflow.sessions.detectIntent' on 'projects/xxxx/agent' denied.

該当のソースコード

Javascript
1//Dialogflow
2
3// projectId: ID of the GCP project where Dialogflow agent is deployed
4const projectId = 'xxxx';
5// sessionId: String representing a random number or hashed user identifier
6const sessionId = '123456789';
7// queries: A set of sequential queries to be send to Dialogflow agent for Intent Detection
8const queries = [
9  'Hello'
10]
11// languageCode: Indicates the language Dialogflow agent should use to detect intents
12const languageCode = 'en';
13
14// Imports the Dialogflow library
15const dialogflow = require('@google-cloud/dialogflow');
16
17// Instantiates a session client
18const sessionClient = new dialogflow.SessionsClient();
19
20async function detectIntent(
21  projectId,
22  sessionId,
23  query,
24  contexts,
25  languageCode
26) {
27  // The path to identify the agent that owns the created intent.
28  const sessionPath = sessionClient.projectAgentSessionPath(
29    projectId,
30    sessionId
31  );
32
33  // The text query request.
34  const request = {
35    session: sessionPath,
36    queryInput: {
37      text: {
38        text: query,
39        languageCode: languageCode,
40      },
41    },
42  };
43
44  if (contexts && contexts.length > 0) {
45    request.queryParams = {
46      contexts: contexts,
47    };
48  }
49
50  const responses = await sessionClient.detectIntent(request);
51  return responses[0];
52}
53
54async function executeQueries(projectId, sessionId, queries, languageCode) {
55  // Keeping the context across queries let's us simulate an ongoing conversation with the bot
56  let context;
57  let intentResponse;
58  for (const query of queries) {
59    try {
60      console.log(`Sending Query: ${query}`);
61      intentResponse = await detectIntent(
62        projectId,
63        sessionId,
64        query,
65        context,
66        languageCode
67      );
68      console.log('Detected intent');
69      console.log(
70        `Fulfillment Text: ${intentResponse.queryResult.fulfillmentText}`
71      );
72      // Use the context from this response for next queries
73      context = intentResponse.queryResult.outputContexts;
74    } catch (error) {
75      console.log(error);
76    }
77  }
78}
79executeQueries(projectId, sessionId, queries, languageCode);