I've implemented Braintree gem (with this help: http://www.sitepoint.com/integrate-braintree-payments-rails/).
In my view I have the "dropin" code:
<div class="form-container radius-box glassy-bg small-10 small-centered medium-8 large-6 columns">
<%= form_tag transactions_path do%>
<p>Please enter your payment details:</p>
<div id="dropin"></div>
<%end%>
</div>
When I remove it, object is being saved. But with this code, the submit button does not do anything. It's very hard to debug - there are no outputs at all ("create" action is not being started).
you need to have a submit button for any form to work.
Add this on your form.