IOS MDM-Managed Settings Command return CommandFormatError

IOS MDM-Managed Settings Command return CommandFormatError

I receive "CommandFormatError" on Managed Settings commands.
That's what I'm sending as a Settings command:
<?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>123456</string>
<key>Command</key>
<dict>
<key>RequestType</key>
<string>Settings</string>
<key>Settings</key>
<array>
<dict>
<key>Item</key>
<string>VoiceRoaming</string>
<key>Enabled</key>
<true/>
</dict>
</array>
</dict>
</dict>
</plist>
Thank you in advance!