Both vCenters should be at the same major version, see: https://storagehub.vmware.com/#!/vsphere-replication/vsphere-replication-faq/introduction-and-general-information-4
Can I use vSphere Replication to replicate a VM between vCenters running different versions of vSphere Replication (eg. VR 5.5 to 6.0)?
To replicate between vCenters, vSphere Replication requires the same major version (eg. 5.5.x > 5.5.x) of vCenter and vSphere Replication at both source and target. This is the only officially tested and supported configuration. Check the VMware Product Interoperability Matrix if you have any questions about matching vCenter and vSphere Replication versions.