The Suspend and Resume feature is in Limited Availability. If you wish to have access to the feature, submit a request at Zuora Global Support.
You can resume a subscription even if the following future-dated amendments already exist on the subscription:
If the effective date of the future-dated amendment is earlier than the subscription resume date, the amendment will not take effect until the subscription is resumed. You can resume a subscription before a future-dated amendment on the subscription from the Zuora UI, SOAP API, and REST API.
See Suspend a Subscription with Future-dated Amendments for the examples.