Installing CodeWorkout on a fresh server, I got an error with the puma gem:
Bundler could not find compatible versions for gem "puma":
In snapshot (Gemfile.lock):
puma (= 4.3.10)
In Gemfile:
puma (~> 4.3.5)
capistrano3-puma was resolved to 6.0.0.beta.1, which depends on
puma (>= 5.1, < 7.0)
Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.
ERROR: Service 'web' failed to build: The command '/bin/sh -c bundle install' returned a non-zero code: 6
It seems like a straightforward version conflict, but I don't have the experience with Ruby to know which way to resolve the dependency.