...

app/controllers/v1/complaints_controller.rb

@@ -39,7 +39,7 @@ class V1::ComplaintsController < ApplicationController
       ComplaintsMailer.new_complaint_received(@complaint, @current_user).deliver_now
       render json: @complaint, status: :created
     else
-      render json: complaint.errors, status: :unprocessable_entity
+      render json: @complaint.errors, status: :unprocessable_entity
     end
   end