How to set secret environment variable on Waypoint using ECS

I tried python application deploy using secret environment variable.

Reading some documents, I understood there are some way to set environment variables.
I did it by setting WP_VAR_token = [here is value]
However, when waypoint up, output include these variable like that,

        VARIABLE       |                     VALUE                     |  TYPE  | SOURCE   
-----------------------+-----------------------------------------------+--------+----------
  token                  | <here is value>                            | string | env

and the variable are not included in ecs service(application cannot get the environment variable!). So I have trouble understooding the logic of passing application environment variables.

Anyone have any insight?
I’m not familiar with this product, so I think it’s possible that I’m making a rudimentary mistake, but I’m at a dead end without even knowing what kind of mistake I’m making, so I’d like to ask you a question here.