As seen below, I have a subscription set to retry 5 times and them move the message to a deadlettering queue. I also have the retry policy set to exponentially back off. This is however not happening. All the config was done using the web console interface.
Is there any reason this is not working? All the above settings seem to just be ignored. Still seems to retry immediately and continuously.
For me, this was because the Pub/Sub service account didn't have permissions. Once they were granted, problem messages were moved to Dead Letters after the specified number of max retries.
Check the Dead Lettering tab for the Subscription: