I have a form that is using form_tag and not sure how to use it with the simple_form gem. This is how my form looks:
form_tag
<%= form_tag create_mult
simple_form is a wrapper around form_for, not form_tag. You can use simple_form_for instead of form_for, but form_tag just creates tags with specified content, it is not relevant to simple form.
form_for
simple_form_for