Scala, Akka Http, Heroku in sbt multi-project - scala

Question

I'm starting with Heroku, I'm a developer that build Rest API using Scala and Akka Http.
Yesterday I was able to create a very simple API and deploy it in Heroku. To do I followed this example: https://dzone.com/articles/akka-http-from-zero-to-heroku-in-10-minutes
Then I decide to add complexity to the API so I created a new project: an sbt multi-project. Usually I do pretty much what is described in this example: https://pbassiner.github.io/blog/defining_multi-project_builds_with_sbt.html. The code of this project is located here: https://github.com/ovats/heroku-akka-multi.
In my local environment the project works fine. I start the service with:
sbt api/run
Then using curl I can make a request:
curl http://localhost:8080
So far so good.
The problem is: I can deploy it to Heroku (git push heroku master) but it wont run.
Using the heroku cli I can see in the logs:
...
2021-11-27T01:06:44.368868+00:00 heroku[web.1]: Starting process with command `target/universal/stage/bin/heroku-akka-multi`
2021-11-27T01:06:46.211834+00:00 app[web.1]: Setting JAVA_TOOL_OPTIONS defaults based on dyno size. Custom settings will override them.
2021-11-27T01:06:46.211994+00:00 app[web.1]: bash: target/universal/stage/bin/heroku-akka-multi: No such file or directory
2021-11-27T01:06:46.339690+00:00 heroku[web.1]: Process exited with status 127
2021-11-27T01:06:46.472410+00:00 heroku[web.1]: State changed from starting to crashed
2021-11-27T01:06:46.475832+00:00 heroku[web.1]: State changed from crashed to starting
...
Ok, I can see bash: target/universal/stage/bin/heroku-akka-multi: No such file or directory. I think this is related to the content of the file Procfile.
Is the problem the Procfile content?
Is the issue somewhere else?
It seems that Heroku does not know how to start the service, maybe where is the main class or something similar to this. What am I doing wrong?
Any help will be appreciated.