Unfortunately, at the moment, implementing the RPC protocol (encapsulated in Shelly endpointId 0xEF, custom cluster 0xFC01, non-standard Zigbee Profile 0xC001) is not possible on Hubitat.
There is a HE platform bug, where Data Type: Character String (0x42) is truncated before being parsed into DescMap - the last 4 bytes are 'eaten' somewhere :
On Hubitat :
Giving up ... 
Actually, it may be not very difficult to fix in HE platfor: there is a 4 positions displacement :
@mike.maxwell