Weebhok sunscription “updated_at” & “retry_started_at” fields

What does mean the fields “updated_at” “retry_started_at” in the Webhook Subscription Object?
I have read the documentation but it is still not clear to me what this data represents. In what way is a subscription updated? I have not found an endpoint to update a webhook subscription, only GET or DELETE.
And in the case of “retry_started_at” what does it mean? I have subscriptions in NULL in that field and others with the same date as “updated_at”. I don't understand it.
Thanks for your time.