I'm not super familiar with the inner workings of ClickBank, but are you the owner of your own ClickBank account? It sounds like the integration may not support affiliate accounts since affiliate API keys don't include PII. It may be worth contacting the ClickBank team to confirm since they own and manage this integration. 

When you say you're hoping to set this up using the instant notification service, are you referring to the scheduled/instant tags on trigger steps? 
https://zapier.com/apps/clickbank/integrations#triggers-and-actions
 

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If so, these tags represent the different trigger types — polling and webhooks. 

The majority of triggers are polling triggers (aka scheduled triggers). With a polling trigger, Zapier will check for new data from your trigger every X minutes based on your plan level. Free and Starter plans are 15 minutes — all other plans vary between 2 minutes to 1 minute. Instant triggers work by using webhooks. Webhooks are automated notifications sent between apps.

Trigger types are defined by the app's API and unfortunately can't be changed. If you're curious, here's a guide with more details on this: https://help.zapier.com/hc/en-us/articles/8496244568589-Types-of-triggers-in-Zaps

Please don't hesitate to reach back out if you have any other questions. I'm here to help!