After migrating zk8.6.0.1 to 9.0 i am facing this error before logging

answered 2020-01-02 10:32:49 +0800

cor3000
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Those errors originate from ZK's (ajax)update requests to /zkau. The < indicates that the response contains HTML instead of the JSON like response ZK's client engine expects - likely an error page with a server error 500 or authentication error 401.

In your browser's network tab you'll see the request to /zkau it will contain the event sent to the server and the response body received from the server. This response body - assuming it is HTML - will also contain a human readable error message.

Also your server side logs could contain some information about what went wrong.