Service_template is previously needed if you want to use template, however an update last year makes it unnecessary to use service_template. You just need service:
Frenck explained “This PR removes the need for service_template & data_template in service and event actions. Instead, service & data now accept templates.”
That solved the puzzle I had, in an automation of my xmas lights in the house. The automation did not return an error but it was with a service_template and it the if then else functioned but no light was turned on. Now I finally changed the template in just service and they worked. Had I seen this little snippet of value information sooner lolz well it would have saved me hours of trying to figure this out.