Thanks for posting to PX Community @Alistair FIeld !
The PX Engagements Webhooks messages do not provide that level of “button” specificity, only that something was “clicked”. I suspect you may already know this if you have tested that option.
For this use case, I would recommend using the PX Custom Event Webhook instead. Other than creating the PX Webhook for that Custom Event, you would need to the necessary JavaScript code to your HTML source code in that Engagement for your button(s). After that, when the Engagement button is clicked a new PX Custom Event is also created, which will be sent as a PX Webhook message to your destination for processing.
Here is some sample Engagement source HTML for doing this is on a button:
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<span class="apt-custom-button" style="color: #ffffff; font-family: Arial, Helvetica, sans-serif;"> <a href="http://www.gainsight.com" onclick="aptrinsic('track', 'LearnMore', {'clicked': 'true'});" rel="noopener noreferrer" style="text-decoration: none; color: inherit;" target="_blank"><span style="text-align: center; line-height: normal; border-radius: 3px ; background-color: #0181c8; padding: 10px 15px 10px 15px; display:inline-block; margin-left: auto; margin-right: auto; cursor: pointer; font-size: 13px;">I want to Learn More</span></a></span>
I hope this helps, Happy PX-ing!!!