How to use Simple HTML in Mailvio

Here is the HTML code:
 

<form action="https://apiv2.mailvio.com/api/addsubscriber?am=ACCOUNTID&fid=FORMID" method="post">
<input type="hidden" name="key" value="YOURAPIHERE"/>
<input type="hidden" name="redirectUri" value="Your redirect URL here"/>
<input type="hidden" name="errorUri" value="Your redirect url here or error URL"/>
<input type="hidden" name="groupId" value="GROUPID"/>
<input type="email" name="emailAddress" value="" placeholder="Enter Email Here" />
<input  class="btn btn-success" type="submit" value="Submit" />
</div>

</form>