Umbrella app and git submodule

I use Emacs and used to use lsp-mode for elixir coding. I an attempt to reduce dependency on external packages as much as possible, I decided to give eglot a shot since it defaults to project.el, flymake and other built-in packages.

Project.el only recognises git repos as projects so when I created an umbrella app, I initialsed a git repo in the parent folder and also in each of the child applications as follows:

|_ apps
     |_ child-app1
     |_ child-app2

However when I try to add the child applications as submodules to git with the command git submodule add ./apps/child-app1, I get the error message:

❯ git submodule add ./apps/child-app1
fatal: not a git repository: ~/Code/elixir/umbrella-app/child-app1/../.git/modules/auction
'child-app1' does not have a commit checked out

I have a feeling it’s got to do with the fact that the folder apps hasn’t been initialised as a git repo. What is the best way to go about this.