You might have missed to add the default url hosts to your environment config-files. When you run the rails g devise:install
command you usually receive those instructions.
# config/environments/development.rb
# Default actiomailer url host (required by devise)
config.action_mailer.default_url_options = { host: 'myapp.dev' }
You need this setting for all your environments.
# config/environments/production.rb
# Default actiomailer url host (required by devise)
config.action_mailer.default_url_options = { host: 'myproductionapp.com' }