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

And When trying to update the publication URL from CMS gets error

(80040301) Unable to save item
Invalid value for property 'PublicationUrl'. The Publication URL '/en' of the Publication with ID 'tcm:0-1010-1' does not match the server-relative URL '' of the Mapping with ID 'Website6'.

`Invalid value for property 'PublicationUrl'. The Publication URL '/en' of the Publication with ID 'tcm:0-1010-1' does not match the server-relative URL '' of the Mapping with ID 'Website6'.`

    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