Because Its assuming you are trying to save value of a User
in new_email
field, that doesn't exist in your users
table. Please use text_field_tag
for this kind of form. you can find the docs here:
<%= form_tag update_user_email_admin_user_path do %>
<%= text_field_tag 'email', nil , placeholder: 'E-mail or user id' %>
<%= text_field_tag 'new_email', nil , placeholder: 'New e-mail' %>
<%= submit_tag "Update email", class: 'btn-1 btn-round btn-size-2' %>
<% end %>
Hope it will help.Thanks