ExCrowdin.API.project_id

You're seeing just the function project_id, go back to ExCrowdin.API module for more information.

In config.exs, use a string, a function or a tuple:

config :ex_crowdin, project_id: System.get_env("CROWDIN_PROJECT_ID")

or:

config :ex_crowdin, access_token: {:system, "CROWDIN_PROJECT_ID"}

or:

config :ex_crowdin, access_token: {MyApp.Config, :crowdin_project_id, []}