Used in conjunction with data-id to specify a non-default API endpoint for retrieving the form definition and submitting the resulting data. This is used mostly for hitting development servers; if you are using
data-form-url you do not need this.
If you are using data-id, and your database instance is accessed by a URL other than
www2.myngp.com, you likely need to use this attribute.
Example, to load the definition and submit to
<div class="ngp-form" data-id="12345" data-endpoint="https://developerboxname.local"></div>