InvalidDeviceSpec: Invalid configuration for device '3'. while adding RDM Disks to VM

I am reconfiguring the VM to add RDM Disks in virtual compatability mode through RbVmomi i.eRuby interface for Vcenter APIs.But I am getting the below error

InvalidDeviceSpec: Invalid configuration for device '3'.

Below is the config I am using

RbVmomi::VIM.VirtualDiskRawDiskMappingVer1BackingInfo(

   :diskMode => "persistent",

   :fileName => "[test-local-storage-1] test/test.vmdk",

   :compatibilityMode => "virtualMode",

   :lunUuid => scsi_lun,

  )

Can anyone please help what could be the issue here?

I am using ESXi 6.5