Event topic template problem!

I would like to use a event topic template as follow:

Event topic template.

event_topic_template=“IOT/{{ .applicationName }}/device/{{ .DevEUI }}/event/{{ .EventType }}”

but does not work and the error in log like this:

level=error msg=“integration/multi: integration error” ctx_id=1bb0658a-317c-4bd3-8c69-7799a1457e2c error=“get topic error: execute template error: template: event:1:7: executing “event” at <.applicationName>: can’t evaluate field applicationName in type struct { ApplicationID uint64; DevEUI lorawan.EUI64; EventType string }” integration="*mqtt.Integration"

Would you can give any suggestion?

Edit: Nm, misread the MQTT topic.

Gateway bridge and network server are not configured with this prefix. I hava error log not about using custom prefix issue, but because I used a custom tag ‘{{ .applicationName }}’ that caused the problem.