MDM “RestartDevice” is not a valid request type.

I am following

https://developer.apple.com/library/content/documentation/Miscellaneous/Reference/MobileDeviceManagementProtocolRef/3-MDM_Protocol/MDM_Protocol.html#//apple_ref/doc/uid/TP40017387-CH3-SW171

for MDM integration.

MDM command request is as follows :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN""http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<?xml version="1.0" encoding="UTF-8"?>
<plist version="1.0">
   <dict>
      <key>Command</key>
      <dict>
         <key>RequestType</key>
         <string>RestartDevice</string>
      </dict>
      <key>CommandUUID</key>
      <string>67e4a33d-f093-450c-b45e-d27d9d577569</string>
   </dict>
</plist>

I am getting following response :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
   <dict>
      <key>CommandUUID</key>
      <string>67e4a33d-f093-450c-b45e-d27d9d577569</string>
      <key>ErrorChain</key>
      <array>
         <dict>
            <key>ErrorCode</key>
            <integer>12021</integer>
            <key>ErrorDomain</key>
            <string>MCMDMErrorDomain</string>
            <key>LocalizedDescription</key>
            <string>“RestartDevice” is not a valid request type.</string>
            <key>USEnglishDescription</key>
            <string>“RestartDevice” is not a valid request type.</string>
         </dict>
      </array>
      <key>Status</key>
      <string>Error</string>
      <key>UDID</key>
      <string>22c4e464e01a3343123ac47634fa9e081f045ff9</string>
   </dict>
</plist>

I am getting this kind of error for some other request type also like ShutDownDevice, EnableLostMode, etc.

I make sure that device's OS version is above required OS version.

Can anyone please let me know what is wrong here?