Your HTML works fine. The <input>
has all the attributes on it that it should. The problem is that your submit button is in the wrong spot. It needs to be inside the form.
Do that, then it works fine. So, basically make your JSON:
{"status": true, "html": "<form id=\"ajax-form\"><input type=\"email\" name=\"email\" required=\"required\" /><input type=\"submit\" value=\"send\" /></form>"}