subscription_not_paused
HTTP 409, type conflict_error.
Only a paused subscription can be resumed.
Why it happened
A resume was requested on a subscription that is not paused. Resume is accepted only from paused, and every other state is refused with this code: pending_first_payment, trialing, active, past_due, canceled, expired and terminated. The message names the subscription's current state.
A paused subscription whose pause behavior cannot be resumed is refused with pause_behavior_unsupported instead.
How to fix it
Read the state in the message. If it is active or trialing, the subscription is already running and no action is needed. If it is pending_first_payment, it is waiting for its first payment and becomes active when that payment succeeds. A subscription with a trial starts in trialing when it is created, before any charge, so it never passes through pending_first_payment. If it is past_due, a renewal payment failed, and it returns to active when a retry of that payment succeeds. Neither needs a resume, and neither accepts one. A canceled, expired or terminated subscription cannot be resumed.
Retrying: do not retry the same request. It will not succeed.