How to get the path to the attachment in the redmine template?

Question

Redmine

I added a custom file field to the user, I want to display a link to this file in the template.
So far, only the file name has been obtained like this:
user.custom_field_values[0].custom_field.cast_value(user.custom_field_values[0].value).filename
Sample valid link: /attachments/download/3/pp.png, this one " 3" can't get it.