I am creating the localization sites /en using the `Set-TtmMapping -RelativeUrl`
but getting the error. Any Suggestion would be highly appreciated.  

    PS C:\Users\mtsuser> Get-TtmMapping
    
    
    CmEnvironmentId     : Tridioncm_1921681216
    PublicationId       : tcm:0-1010-1
    EnvironmentPurpose  : Staging
    WebApplicationId    : Website6_RootWebApp
    RelativeUrl         : /
    PrimaryMappedUrl    : http://dxa.com/
    IsOffline           : False
    CdEnvironment       : 
    Id                  : Website6
    ExtensionProperties : {}


    PS C:\Users\mtsuser> Set-TtmMapping -RelativeUrl en
    cmdlet Set-TtmMapping at command pipeline position 1
    Supply values for the following parameters:
    (Type !? for Help.)
    Id: Website6
    Set-TtmMapping : The server-relative URL '/en' of the Mapping does not match the Publication URL property '/' of the Publication 'tcm:0-1010-1'.
    At line:1 char:1
    + Set-TtmMapping -RelativeUrl en
    + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        + CategoryInfo          : NotSpecified: (Tridion.Topolog...tMappingCommand:SetMappingCommand) [Set-TtmMapping], DataServiceException
        + FullyQualifiedErrorId : Tridion.TopologyManager.Automation.Cmdlets.SetMappingCommand