Deploying to Heroku

I’ve followed all of the documentation I can find regarding deploying to Heroku but am failing with a Mix.Config.LoadError

Relevant output from git push heroku master

remote: -----> Fetching app dependencies with mix
remote: ** (Mix.Config.LoadError) could not load config config/prod.secret.exs
remote:     ** (File.Error) could not read file             
"/tmp/build_d088e34b7a47fecac9bbe69a031fa7e5/config/prod.secret.exs": no such file or 
directory
remote:     (elixir) lib/file.ex:272: File.read!/1
remote:     (mix) lib/mix/config.ex:180: Mix.Config.read!/2
remote:     (mix) lib/mix/config.ex:217: anonymous fn/3 in Mix.Config.read_wildcard!/2
remote:     (elixir) lib/enum.ex:1811: Enum."-reduce/3-lists^foldl/2-0-"/3
remote:     (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6
remote:     (stdlib) erl_eval.erl:878: :erl_eval.expr_list/6
remote:     (stdlib) erl_eval.erl:404: :erl_eval.expr/5
remote:  !     Push rejected, failed to compile Elixir app.
remote: 
remote:  !     Push failed

So, it appears to be failing when it fails to find prod.secret.exs, however, as per the docs this file is no longer in use, doesn’t get imported anywhere and doesn’t exist in the repo any longer.

Not sure why I’m having this issue, any help would be greatly appreciated.

Thanks