Hello!
@Sergiu.Daniluk is absolutely correct here - both Nexus switches that form a vPC domain must be of the same generation. Furthermore, Cisco only supports a vPC domain where both Nexus switches are the exact same model. This is called out under the "Guidelines and Limitations" heading of the "Configuring vPCs" chapter in the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide document:
"When forming a vPC domain between two Cisco Nexus 9300 Series switches, both switches must be the exact same model to form a supported vPC domain. When forming a vPC domain between two Cisco Nexus 9500 Series switches, both switches must consist of the same models of line cards, fabric modules, supervisor modules, and system controllers inserted in the same slots of the chassis to form a supported vPC domain."
I hope this is helpful - thank you!
-Christopher
