Custom configuration profile error

[J. J.]

I have created a custom configuration profile following Apple's reference guide. You can find a model of the .mobileconfig file here:

<?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>ConsentText</key>
    <dict>
        <key>default</key>
        <string>Consent text here.</string>
        <key>en</key>
        <string>Consent text here.</string>
    </dict>
    <key>PayloadContent</key>
    <array>
        <dict>
            <key>PayloadContent</key>
            <array>
                <dict>
                    <key>DefaultsData</key>
                    <dict>
                        <key>PreferenceKeyHere</key>
                        <true/>
                    </dict>
                    <key>DefaultsDomainName</key>
                    <string>com.apple.springboard</string>
                </dict>
            </array>
            <key>PayloadIdentifier</key>
            <string>com.payload.identifier.here</string>
            <key>PayloadType</key>
            <string>com.apple.defaults.managed</string>
            <key>PayloadUUID</key>
            <string>XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX</string>
            <key>PayloadVersion</key>
            <integer>1</integer>
        </dict>
    </array>
    <key>PayloadDescription</key>
    <string>Payload description here.</string>
    <key>PayloadDisplayName</key>
    <string>Profile name here.</string>
    <key>PayloadIdentifier</key>
    <string>com.identifier.here</string>
    <key>PayloadOrganization</key>
    <string>Organization Inc.</string>
    <key>PayloadRebootSuggested</key>
    <true/>
    <key>PayloadType</key>
    <string>Configuration</string>
    <key>PayloadUUID</key>
    <string>YYYYYYYY-YYYY-YYYY-YYYY-YYYYYYYYYYYY</string>
    <key>PayloadVersion</key>
    <integer>1</integer>
</dict>
</plist>

For some reason I get an "unknown error" when trying to install it on a device. I double-checked everything and I couldn't find anything wrong with the profile, which is also considered "valid" by Xcode and Apple Configurator. Any ideas? Thank you.