Front-end form, creating a tag
It looks like you are not targeting the action URL. When accessing a Craft controller, you'll need to use the actionTrigger in your URL:

Your current URL:

http://talkbox.es:8888/index.php/tags/createTag


Should be updated to:

http://talkbox.es:8888/index.php/actions/tags/createTag


The actionTrigger is configurable so if you plan to reuse your code on multiple sites, you won't want to hard code that value. In twig, you can output that value using the craft.config variable:

{{ craft.config.actionTrigger }}