You can use vSphere Replication with certain editions of vSphere that include vSphere Replication in the license.
vSphere Replication does not have a separate license as it is a feature of certain vSphere license editions.
vSphere Essentials Plus
vSphere Enterprise Plus
If you have the correct vSphere license, there is no limit on the number of virtual machines that you can replicate by using vSphere Replication.
You cannot use vSphere Replication to replicate virtual machines on ESXi hosts that do not have the correct vSphere license. If you install vSphere Replication on an ESXi host that does not have the correct license and try to configure replication for virtual machines on that host, the replication fails with a licensing error.
If you configure a virtual machine for replication on a host with the correct vSphere license and move it to a host with an unsupported license, vSphere Replication stops replication of that virtual machine. You can disable vSphere Replication on a configured virtual machine on the unlicensed host.