So I’m seeing a very odd bug with the Guest API implementation. We’re building a custom chat interface in ServiceNow that bypasses the standard Messenger widget. The goal is to use the Guest API to authenticate and then post messages directly to Genesys Cloud. I’ve got the OAuth token exchange working fine. The client gets a valid access token from /api/v2/oauth/token using the client_credentials grant. The token looks good. I can hit the GET endpoints for queue availability without issue.
The problem hits when I try to send a message. I’m hitting POST /api/v2/conversations/messages with the conversation ID I got from the initial guest connection. The request body is standard JSON:
{
"text": "Hello support",
"language": "en-US"
}
The headers include the Authorization: Bearer <token> and Content-Type: application/json. The response is a hard 401 Unauthorized. The error payload is vague:
{
"code": "unauthorized",
"message": "User is not authorized"
}
I’ve checked the scopes on the OAuth client. It has conversation:read, conversation:write, and guest:access. I thought conversation:write was enough. The documentation says the Guest API uses a specific flow where the guest ID is part of the token claims. Maybe the token generated via client_credentials doesn’t have the guest context attached? I tried switching to password grant but that feels wrong for a server-side integration. The ServiceNow backend is running in Toronto timezone, so time drift isn’t the issue. The token is fresh. I’m stumped. Is there a specific header I’m missing for the Guest API message post? Or do I need to use a different endpoint for initial message send?
scope: “webchat:guest:write”
This is caused by using `client_credentials` which doesn't inherit guest scopes. you need the specific `webchat:guest:write` scope on that token.
// Switch to client_credentials with specific guest scope
cfg := platformclientv2.NewConfiguration()
cfg.SetAuthMode(“oauth”)
cfg.SetClientId(os.Getenv(“CLIENT_ID”))
cfg.SetClientSecret(os.Getenv(“CLIENT_SECRET”))
// Ensure webchat:guest:write is in the scope request
If I remember correctly, the token just needs that explicit scope. `client_credentials` works fine if you pass `webchat:guest:write` during the exchange. the 401 vanishes immediately.
Take a look at at the token payload itself. decoding the jwt shows exactly which scopes are attached. if you’re using the python sdk, it’s easy to debug this locally before pushing to prod.
import jwt
import json
# assuming you have the raw token string
token = "your_access_token_here"
# decode without verification to inspect claims
claims = jwt.decode(token, options={"verify_signature": False})
# check for the specific guest scope
if "webchat:guest:write" in claims.get("scope", []):
print("scope is present")
else:
print("missing scope: webchat:guest:write")
print("current scopes:", claims.get("scope", []))
the issue usually isn’t the grant type itself, but how the client configures the scope request. in terraform, when you define the genesyscloud_oauthclient resource, you have to explicitly list webchat:guest:write in the scopes argument. if you rely on defaults or copy-paste from a standard integration client, it often misses this.
resource "genesyscloud_oauthclient" "guest_chat" {
name = "guest-chat-integration"
description = "for servicenow guest api"
type = "confidential"
scopes = [
"webchat:guest:write",
"webchat:guest:read",
"conversation:webchat"
]
redirect_uris = ["https://your-domain/callback"]
}
also double check the client secret rotation. sometimes the token is valid but the backend service has cached an old key. i’ve seen this in staging where the api gateway hasn’t synced with the auth service yet. run a terraform plan on the oauth client resource to see if there are drifts. if the scope is correct and you still get 401, it’s likely a permissions issue on the underlying routing queue or webchat configuration. the guest user needs to be able to start a conversation in that specific queue.