Nope, my mistake. Turns out RetryPolicy doesn't work well if you don't actually feed it into the SubscriptionConfig :( .
It doesn't seem possible to affect the retrypolicy of a subscription at all through the go pubsub package.
https://pkg.go.dev/cloud.google.com/go/pubsub#SubscriptionConfig includes a retrypolicy, which has a minimum and maximum backoff, but if you set these, and create a new subscription, the subscription will have a retry policy of immediate.
Is there anyway to set the retry policy of a pubsub subscription using the go pubsub package?
Go Pub/Sub library maintainer here. Could you paste your code here?
You should be able to create a Subscription with a RetryPolicy without needing to update it after creation.