Signup form in your web page

embed_signup.html

<form action="https://API_HOST/save" method="POST">
  <input type="hidden" name="organization_KEY" value="5881"/>
  <input type="hidden" name="chapter_KEY" value="887"/>
  <input type="hidden" name="email_trigger_KEYS" value="12644,12656"/>
  <input type="hidden" name="object" value="supporter"/>
  <input type="hidden" name="Receive_Email" value="1"/>
  <label for="first_name">First Name:</label><input type="text" id="first_name" name="First_Name"/><br/>
  <label for="last_name">Last Name:</label><input type="text" id="last_name" name="Last_Name"/><br/>
  <label for="email">Email:</label><input type="text" id="email" name="Email"/><br/>
  <style>.memberCode{display:none;}</style>
  <div class="memberCode"> Optional Member Code <input name="first_name_949" value=""/></div>
  <input type="hidden" name="link" value="groups"/>
  <input type="hidden" name="linkKey" value="13"/>
  <input type="hidden" name="tag" value="excellent"/>
  <input type="hidden" name="redirect" value="http://YOUR URL"/>
  <input type="Submit" value="Sign up" />
</form>

Some of your br tags are broken... </br> should be <br/>

Also you are missing a closing slash on this line:
<input type="hidden" name="redirect" value="http://YOUR URL">

Thanks, @microcosm. I'll fix those now.