Rails foreign key issue in Heroku migrate with Postgres - ruby-on-rails

Question

I am trying to deploy a Rails project with Heroku.
In development I am running the Ruby project on AWS Educate Cloud9 and using Sqlite3 as the database.
I can successfully run the Rails project on AWS and migrations work fine also there
$ rails db:migrate
In Production the database is postgres.
This is the Gemfile
source 'https://rubygems.org'
git_source(:github) do |repo_name|
repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
"https://github.com/#{repo_name}.git"
end
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.0.7', '>= 5.0.7.2'
# Use sqlite3 as the database for Active Record
#gem 'sqlite3', '~>1.3.0'
#gem 'devise' , '~>4.3.0'
gem 'devise', git: 'https://github.com/plataformatec/devise' #, ref: '88e9a85'
# Use Puma as the app server
gem 'puma', '~> 3.0'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug', platform: :mri
gem 'sqlite3', '~>1.3.0'
end
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '~> 3.0.5'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
end
group :production do
gem 'pg'
end
# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
Using,
$ bundle update
$ bundle install --without production
$ git add .
$ git commit -m "blah"
$ git push origin master
$ git push heroku master
$ heroku run rails db:migrate
This gives an error which tells me that there is an issue with a foreign key, but when I db:migrate in development there is no issue with a foreign key. I only seem to get this error when I migrate in Heroku using 'pg'.