Metricbeat 7.2.1 custom index name: missing field accessing 'output.elasticsearch.index'

[brandnull]

Hello, I'm trying to set up Metricbeat in different instances, gathering metrics in a single Elasticsearch node. However, I want to set up a custom index pattern per instance. In
In /etc/metricbeat/metricbeat.yml I have the following:

setup.ilm.enabled: false
output.elasticsearch.index: "kafka-dev-metricbeat-${[agent.version]}-%{+yyyy.MM.dd}"
setup.template.name: "kafka-dev-metricbeat"
setup.template.pattern: "kafka-dev-metricbeat-*"

If I don't use add the last three lines about output.elasticsearch.index and setup.template, then it works for a single instance. However, if I add those lines and try to start metricbeat, then it fails with the following error:
ERROR instance/beat.go:877 Exiting: missing field accessing 'output.elasticsearch.index' (source:'/etc/metricbeat/metricbeat.yml')

I can't find anything regarding this in the docs or forums, so any pointers regarding this are welcome. Thank you beforehand.

[brandnull]

Solved it by changing output.elasticsearch.index: "kafka-dev-metricbeat-${[agent.version]}-%{+yyyy.MM.dd}" to output.elasticsearch.index: "kafka-dev-metricbeat-%{[agent.version]}-%{+yyyy.MM.dd}".

However, when I start the service, it does not create the new index.