@Nguyen Thuan An You need to update the sample-workitems
with the correct eventhub name that is created on your event hub namespace for which you want to trigger your function.
You can navigate to your event hub resource in azure portal and then navigate to Event Hubs
under the entity of your namespace. Now it will list the number of event hubs that are present on your namespace.
As you can see in my namespace there are multiple eventhubs and I have used iotevents hub in the configuration of my azure app. Similarly you need to update the right eventhub name for your namespace.
The error is expected as the event hub name is incorrect and doesn't exists in your namespace. Feel free to get back to me if you need any assistance.
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