I came across this forum post. Which would indicate that customerio-ruby relays the apns dictionary to the mobile device. But I have had no luck doing so.

I reported an issue to the customerio-ruby repo: https://github.com/customerio/customerio-ruby/issues/113

I’m sure it’s something obvious, but have had no luck after reading this documentation that labels the properties to enable this functionality: https://customer.io/docs/journeys/transactional-api/#parameters-supported-by-the-transactional-push-api