Create Office365 Communication Site

CreateCommunicationSite.ps1

#[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.dll")
#[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Runtime.dll")
#[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.Online.SharePoint.Client.Tenant.dll")
Add-Type -Path "c:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"
Add-Type -Path "c:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\SharePoint Client Components\16.0\Assemblies\Microsoft.Online.SharePoint.Client.Tenant.dll"

function Connect-SPO ([string] $Username, [string]$Password, [string]$TenantUrl) {

    $Context = New-Object Microsoft.SharePoint.Client.ClientContext($TenantUrl)
    $Context.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Username, $(ConvertTo-SecureString -AsPlainText $Password -Force))
    $Context.ExecuteQuery()

    $AuthenticationCookie = $Context.Credentials.GetAuthenticationCookie($TenantUrl, $true)
    $WebSession = New-Object Microsoft.PowerShell.Commands.WebRequestSession
    $WebSession.Credentials = $Context.Credentials
    $WebSession.Cookies.SetCookies($TenantUrl, $AuthenticationCookie)

    $FormsDigest = $Context.GetFormDigestDirect()
    $WebSession.Headers['X-RequestDigest'] = $FormsDigest.DigestValue

    $Context.Dispose()
    return $WebSession
}


function Invoke-RestSPO ([Microsoft.PowerShell.Commands.WebRequestSession] $Session, [string]$RequestUrl, [string]$Method = "Get", [string]$Payload = $null) {
    $Headers = @{ 
        'accept'       = 'application/json;odata=verbose'
        'content-type' = 'application/json;odata=verbose' 
    }

    if ($Method -eq "Post") {
        $Headers['X-RequestDigest'] = $Session.Headers['X-RequestDigest']
        $Response = Invoke-RestMethod -Method $Method -WebSession $Session -Headers $Headers -ContentType "application/json;odata=verbose;charset=utf-8" -Body $Payload -Uri $RequestUrl  -UseDefaultCredentials
    }
    else {
        $Response = Invoke-RestMethod -Method $Method -WebSession $Session -Headers $Headers -ContentType "application/json;odata=verbose;charset=utf-8" -Uri $RequestUrl  -UseDefaultCredentials
    }
    return $Response
}



function Create-CommunicationSite ([Microsoft.PowerShell.Commands.WebRequestSession] $Session, [string]$TenantUrl, [string]$Title, [string]$SiteUrl, [string]$SiteTemplate) {

    $siteTemplateIds = @{ 
        "Topic" = ""
         "Showcase" = "6142d2a0-63a5-4ba0-aede-d9fefca2c767" 
         "Blank" = "f6cc5403-0d63-442e-96c0-285923709ffc"
    }     
    
    $siteCreationRequest = @{
        request = @{
            __metadata                    = @{'type' = 'SP.Publishing.PublishingSiteCreationRequest' }; 
            Title                         = $Title; 
            Description                   = ""; 
            Url                           = $SiteUrl;
            Classification                = "";
            AllowFileSharingForGuestUsers = $false;
        }
    } 

    if($SiteTemplate -ne "Topic"){
      $siteCreationRequest.request.SiteDesignId = $siteTemplateIds[$SiteTemplate]
    }
    $siteCreationRequestJson = $siteCreationRequest | ConvertTo-Json

    $requestUrl = "$($TenantUrl)_api/sitepages/publishingsite/create"
    $data = Invoke-RestSPO -Session $Session -RequestUrl $requestUrl -Method "Post" -Payload $siteCreationRequestJson
    return $data
}

Usage

$TenantUrl = "https://contoso.sharepoint.com/"
$Username = "--username--"
$Password = "---password--"

$session = Connect-SPO -Username $Username -Password $Password -TenantUrl $TenantUrl
$result = Create-CommunicationSite -Session $session -TenantUrl $TenantUrl -SiteUrl "https://contoso.sharepoint.com/sites/mycommsite" -Title "My Communication Site" -SiteTemplate "Topic"
Write-Output "Communication site has been created at: $($result.d.Create.SiteUrl)"