so… I am building one “simple” script, to perform notifications - based on input_booleans switched on or off in the frontend. just to have one thing that displays info on different platforms, for different family members.
tried, and failed at first attempt 
my “notification_script.yaml” contents:
sequence:
- service_template: >-
{% if is_state('input_boolean.bln_notifyjoin', 'on') %}
data_template:
title: "{{ var_temat }}"
message: "{{ var_tresc }}"
data: {"icon":"{{ var_ikona }}"}
{% endif %}
entity_id: notify.ntf_join
<...and here goes more service_templates build in a same way>
all the var_* are texts in variables.
after running that script I’ve got this error: ERROR (MainThread) [homeassistant.helpers.service] Template rendered invalid service: and the whole data_template: contents goes here.
what I did wrong?