HitPay.API.salt

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

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

config :hit_pay, salt: System.get_env("HIT_PAY_SALT")

or:

config :hit_pay, salt: {:system, "HIT_PAY_SALT"}

or:

config :hit_pay, salt: {MyApp.Config, :HIT_PAY_SALT, []}