According to the official Pure Storage FlashArray Asynchronous Replication Configuration and Best Practices Guide, the proper and immediate method to halt an active, in-progress asynchronous replication transfer is by disallowing the protection group at the target.
When you navigate to the target FlashArray and disallow the specific Protection Group, Purity immediately breaks the replication authorization for that group. If there is an in-progress snapshot transfer occurring at that exact moment, the transfer is immediately stopped, and the partially transferred snapshot data is discarded on the target side.
Here is why the other options are incorrect:
Disabling the replication schedule (B): Toggling the replication schedule to "Disabled" only prevents future scheduled snapshots from being created and sent. It does not kill or interrupt a replication transfer that is already currently in progress.
Removing the volume member from a protection group (A): Modifying the members of a protection group updates the configuration for the next snapshot cycle. It does not actively abort the transmission of the current point-in-time snapshot that the array is already busy sending over the WAN.