Guest API /api/v2/conversations/messaging 403 without Messenger Widget

Could someone explain why my Node.js script gets a 403 when calling POST /api/v2/conversations/messaging/{id}/messages directly? I am bypassing the widget to build a custom CLI client. I generate a valid OAuth token and pass it in the Authorization header. The docs say:

“Guest access tokens can be used to send and receive messages on behalf of a guest user.”

My code uses the genesyscloud-platform-client SDK. It works for fetching conversations but fails on sending. Am I missing a specific scope or header?

If I remember right, the 403 happens because the guest token lacks the specific messaging:conversation:write scope required for direct API calls. The widget handles this internally, but your CLI needs explicit permission.

1. Verify your OAuth client has messaging:conversation:write and messaging:guest:send scopes.
2. Generate the guest token via /api/v2/oauth/guest/token with the correct client_id and client_secret.
3. Use the resulting access_token in the Authorization: Bearer header.

Here is a working Node.js snippet using axios to verify the token scope before posting:

const axios = require('axios');

const sendGuestMessage = async (convId, message, token) => {
 const config = {
 headers: {
 'Authorization': `Bearer ${token}`,
 'Content-Type': 'application/json'
 }
 };
 
 try {
 const res = await axios.post(
 `https://api.mypurecloud.com/api/v2/conversations/messaging/${convId}/messages`,
 { text: message },
 config
 );
 console.log('Sent:', res.data.id);
 } catch (err) {
 console.error('Failed:', err.response?.data?.errors);
 }
};

Check the error payload for insufficient_scope if it still fails.

Have you tried verifying the specific OAuth scopes attached to your guest token? The suggestion above regarding messaging:conversation:write is correct, but it is often insufficient on its own for direct API calls.

1. Ensure your OAuth application has both messaging:conversation:write and messaging:guest:send.
2. When generating the guest token via POST /api/v2/oauth/guest/token, explicitly include these scopes in the scope parameter of the request body.
3. Use the PureCloudPlatformClientV2 SDK to validate the token details immediately after generation.

Here is how I check the active scopes in Node.js:

const platformClient = require('@genesyscloud/genesyscloud').platformClient;
const auth = platformClient.AuthApi();

async function checkScopes() {
 const token = await auth.getAccessToken();
 console.log('Active Scopes:', token.scope.split(' '));
}
checkScopes();

If messaging:guest:send is missing, the API will reject the message payload with a 403, regardless of valid authentication. This is a common trap when bypassing the standard widget flow.

check your guest token generation payload. you need to explicitly pass the required scopes in the scope field of the POST /api/v2/oauth/guest/token request body, not just rely on the client default.

{
 "client_id": "your_client_id",
 "scope": "messaging:conversation:write messaging:guest:send"
}

I typically get around this by ensuring the scope array in the guest token request explicitly includes both messaging:conversation:write and messaging:guest:send, as the SDK defaults often omit the write permission.

Warning: Guest tokens expire quickly, so implement a refresh handler in your CLI or you’ll hit 401s mid-session.