Hi Carlos,
It sounds like the index template for the APM indices is missing. Running the following command should show you a list of the APM index templates:
GET _template/apm*
Normally the template is created automatically when starting apm-server. Can you restart apm-server and look for template/load.go:129, and what message it says. For instance:
INFO template/load.go:129 Template already exists and will not be overwritten.
Please view apm-server.yml and ensure the following options are not disabled - they are enabled by default:
setup.template.enabled: true
setup.template.overwrite: true
How did you install apm-server? And did you upgrade from a previous version?