Hey @Tom Farren,
So the most important thing to understand would be how the information is passed to Klaviyo when a member of the website cancels their paid monthly subscription. If this is tracked as an event metric, we can use that event metric to trigger the flow. Guide to Creating a Metric-Triggered Flow
Depending on what platform or plug in you’re using, here are a few from our help center.
Using WooCommerce Subscriptions Data in Campaign and Flows
How to Integrate with ReCharge
How to Integrate with Chargebee
Guide to Integration a Subscription Ecommerce Platform
If this is being passed as a custom profile property as opposed to a metric/event, you could create a segment that has the criteria of whatever that property is being stored in Klaviyo as and can create a segment triggered flow if that information is not coming through as a metric. Guide to Creating a Segment Triggered Flow
Hope that helps point you in the right direction.