Hello,
Custom fields are not currently supported at this time with the plugin. However, you can embed the knowledge tags script into your page:
<script async defer src="https://knowledgetags.yextpages.net/embed?key=<SECRET_KEY>&account_id=<ACCOUNT_ID>&location_id=<LOCATION_ID>" type="text/javascript"></script>
and embed a custom field like this:
<[HTML_TAG] data-yext-field="customFields.[ID]"></[HTML_TAG]>
With documentation here: https://developer.yext.com/docs/guides/working-knowledge-tags/#script
Please let me know if you have any further questions.
Thank you,
Noah
