Access token from Global OAuth Client got forbidden error

We could use the "zendesk access token" for a while, but it failed suddenly in push request. It worked before.

POST /api/v2/any_channel/push.json

{"title":"Forbidden","message":"You do not have access to this page. Please contact the account owner of this help desk for further help."}

What is the reason of this error?

https://developer.zendesk.com/apps/docs/channels-framework/push#calling-the-push-endpoint

• The Global OAuth client was accepted about 2 years ago.
• The channel integration account is active.
• Not all subdomains failed. Only one subdomain failed.