Yes, looks like you are correct, though in my local it works fine but I am getting some exceptions in logs due to fallback controller. Not sure if that could be the cause of the failure in azure environment.
I am getting such error in logs:-
[error] #PID<0.3298.0> running MyFutureNowWeb.Endpoint (connection #PID<0.3297.0>, stream id 1) terminated
Server: localhost:4000 (http)
Request: POST /api_v2/pension/create
** (exit) an exception was raised:
** (FunctionClauseError) no function clause matching in MyFutureNowWeb.FallbackController.call/2
(my_future_now 4.0.0) lib/my_future_now_web/controllers/fallback_controller.ex:8: MyFutureNowWeb.FallbackController.call(%Plug.Conn{adapter: {Plug.Cowboy.Conn, :...}, assigns: %{user_signed_in?: true}, before_send: [#Function<0.28762384/1 in Plug.CSRFProtection.call/2>, #Function<2.77894870/1 in Phoenix.Controller.fetch_flash/2>, #Function<0.32542428/1 in Plug.Session.before_send/2>, #Function<0.66442134/1 in Plug.Telemetry.call/2>, #Function<0.92375621/1 in Phoenix.LiveReloader.before_send_inject_reloader/2>], body_params: %{"employee_pension" => %{"creation_journey_type" => "employer", "current_employment" => "false", "end_year" => "2010", "pension_provider_id" => "", "proposed_employer_name" => "ABC Limited", "proposed_policy_number" => "", "start_year" => "2007"}}, cookies: %{}, halted: false, host: "localhost", method: "POST", owner: #PID<0.3298.0>, params: %{"employee_pension" => %{"creation_journey_type" => "employer", "current_employment" => "false", "end_year" => "2010", "pension_provider_id" => "", "proposed_employer_name" => "ABC Limited", "proposed_policy_number" => "", "start_year" => "2007"}}, path_info: ["api_v2", "pension", "create"], path_params: %{}, port: 4000, private: %{MyFutureNowWeb.Router => {[], %{Bamboo.SentEmailViewerPlug => ["sent_emails"]}}, :phoenix_action => :create, :phoenix_controller => MyFutureNowWeb.APIV2.PensionController, :phoenix_endpoint => MyFutureNowWeb.Endpoint, :phoenix_flash => %{}, :phoenix_format => "json", :phoenix_layout => {MyFutureNowWeb.LayoutView, :app}, :phoenix_router => MyFutureNowWeb.Router, :phoenix_view => MyFutureNowWeb.APIV2.PensionView, :plug_session => %{}, :plug_session_fetch => :done, :plug_session_info => :ignore}, query_params: %{}, query_string: "", remote_ip: {127, 0, 0, 1}, req_cookies: %{}, req_headers: [{"accept", "*/*"}, {"accept-encoding", "gzip, deflate, br"}, {"accept-language", "en-US,en;q=0.9"}, {"authorization", "Bearer SFMyNTY.g3QAAAACZAAEZGF0YW0AAAAkN2VhZjM1NmUtNTE0MS00ZTJiLTkwZDctMTRkNzgwYjViZTJlZAAGc2lnbmVkbgYADKLsbXQB.-yVqBqUSsRJtflbU-rit8j205c3Hb1fwnH8ysNhKlxs"}, {"cache-control", "no-cache"}, {"connection", "keep-alive"}, {"content-length", "321"}, {"content-type", "application/json"}, {"host", "localhost:4000"}, {"origin", "chrome-extension://fhbjgbiflinjbdggehcddcbncdddomop"}, {"postman-token", "d4922bac-7f43-4b65-2d7e-fb0bcc137c92"}, {"sec-fetch-dest", "empty"}, {"sec-fetch-mode", "cors"}, {"sec-fetch-site", "none"}, {"user-agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36"}], request_path: "/api_v2/pension/create", resp_body: nil, resp_cookies: %{}, resp_headers: [{"cache-control", "max-age=0, private, must-revalidate"}, {"x-request-id", "FjLSWGVBjfYwu7kAAOxx"}], scheme: :http, script_name: [], secret_key_base: :..., state: :unset, status: nil}, {:ok, %MyFutureNow.Task{__meta__: #Ecto.Schema.Metadata<:loaded, "tasks">, admin_assignee: #Ecto.Association.NotLoaded<association :admin_assignee is not loaded>, admin_assignee_id: nil, admin_author: #Ecto.Association.NotLoaded<association :admin_author is not loaded>, admin_author_id: nil, body: nil, completed: false, completed_at: nil, completion_pension_status: "verify_customer_details", customer_pension: #Ecto.Association.NotLoaded<association :customer_pension is not loaded>, customer_pension_id: 844, due_date: ~D[2020-09-09], id: 457, inserted_at: ~N[2020-09-08 13:35:00.876097], priority: 1, snooze_count: 0, subject: "LexisNexis IDU FAIL, issue email to customer, set pensions to On Hold", updated_at: ~N[2020-09-08 13:35:00.876097], user: #Ecto.Association.NotLoaded<association :user is not loaded>, user_id: 521, uuid: "7bb33496-6690-4780-955a-3852d0d49938"}})