Deploying Go app to heroku error

I refactored my code file structure to be under the cmd folder since I now added a worker and now it has this structure:

All the go files are inside the folders so in order to install it locally I use 'make install' which I configured to go install each package.
But when I try to push to Heroku it just runs go install and so I get the error:

> Running: go install -v -tags heroku . can't load package: package
> github.com/heroku/secretly-sender: no buildable Go source files in
> /tmp/tmp.pTW8NahxGm/.go/src/github.com/heroku/secretly-sender

How can I fix this?
Here are my other files

Procfile:

web: secretly-sender-web
worker: secretly-sender-worker

Dockerfile:

FROM alpine:latest

WORKDIR "/opt"

ADD .docker_build/secretly-sender /opt/bin/secretly-sender/cmd
ADD ./templates /opt/templates
ADD ./static /opt/static

CMD ["/opt/bin/secretly-sender/cmd"]

Makefile

GO_BUILD_ENV := GOOS=linux GOARCH=amd64
DOCKER_BUILD=$(shell pwd)/.docker_build
DOCKER_CMD=$(DOCKER_BUILD)/secretly-sender/cmd

$(DOCKER_CMD): clean
    mkdir -p $(DOCKER_BUILD)
    $(GO_BUILD_ENV) go build -v -o $(DOCKER_CMD) .

clean:
    rm -rf $(DOCKER_BUILD)

heroku: $(DOCKER_CMD)
    heroku container:push web
    heroku container:push worker

install:
    go install github.com/heroku/secretly-sender/cmd/secretly-sender-web
    go install github.com/heroku/secretly-sender/cmd/secretly-sender-worker
    go install github.com/heroku/secretly-sender/shared

build:
    go build github.com/heroku/secretly-sender/cmd/secretly-sender-web
    go build github.com/heroku/secretly-sender/cmd/secretly-sender-worker
    go build github.com/heroku/secretly-sender/shared

I don't really understand what these files and path mean so I still couldn't solve my issue
Thank you very much!

The answer was to add this:

"heroku": {
	"install": [
		"./cmd/..."
	]
},

to vendor/vendor.json