It does not look like the code in the blog You are following… which looks like this

def create(conn, %{"business" => business_params}) do
  with {:ok, %Business{} = business} <- Directory.create_business(business_params) do
    conn
    |> put_status(:created)
    |> put_resp_header("location", business_path(conn, :show, business))
    |> render("show.json", business: business)
  end
end

Anyway, I would not recommend to follow this (old) post because things have changed since.

Maybe try this one, which cover Phoenix 1.5

https://lobotuerto.com/blog/building-a-json-api-in-elixir-with-phoenix/

BTW You are using user variable, which was never defined, and You define user_params, which is never used.

Your create function is not matching the parameters that you are sending via curl. A possible fix is to change the first line from:

def create(conn, %{"user" => user_params}) do

to:

def create(conn, %{"accounts" => user_params}) do

Although personally i prefer to do little to no matching in controller function heads because I find the no function clause matching not very informative. If you changed your create to function to:

def create(conn, params) do
  %{"user" => user_params} = params
  ...
end

Then you would have gotten a more informative pattern matching error.