Deploy Docker, problems parsing your heroku.yml: empty

I trying to deploy a React App on heroku with a heroku.yml using a Dockerfile. But whe i try to deploy it, i get "problems parsing your heroku.yml" with no error

front/Dockerfile

WORKDIR /app
COPY package.json ./
COPY yarn.lock ./
RUN yarn install --frozen-lockfile
COPY . .
RUN yarn build

FROM nginx:1.19-alpine AS server
COPY ./etc/nginx.conf /etc/nginx/conf.d/default.conf
COPY --from=builder ./app/build /usr/share/nginx/html
CMD ["nginx", "-g", "daemon off;"]

heroku.yml

build:
  docker:
    release:
        dockerfile: ./front/Dockerfile
        target: builder
    run:
        dockerfile: ./front/Dockerfile
        target: server
release:
  image: builder
run:
  image:
    command:
    image: server

Error on build log:

=== Fetching app code
=!= There were problems parsing your heroku.yml. We've detected the following issues:

I don't understand why i get that.