You are trying to read data from a subscription that is configured as Push, rather than pull.
Push subscriptions send the messages through a configured https endpoint: there is no need to read the data.
If you need to read data from a pubsub topic , you must use a pull subscription instead.
Remember: messages get published into a pubsub topic. You can have more than one subscription to read that messages.
If you have a push subscription, probably it is also a good idea to have a pull one configured (with low retention = because it cost money) just to be able to see what was sent by the push subscription.
When reading from pubsub with
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